roll label printers are ideal for printing netstamps ™ style of postage indicia . a problem with printing netstamps ™ however , is ensuring that users correctly provide the serial number into software before printing is initiated , because if the wrong serial number is put into software , the printed netstamps ™ will be defective . with roll label printers , once a roll is loaded into the printer , it is difficult for the user to see the serial number on the label . this problem is not experienced with unprinted sheets of netstamps ™ labels , which a user handles before being placed into conventional label printers . the system of the invention provides a way for users to determine what is the serial number of a leading label of the currently loaded roll of netstamps ™ labels , and thereby avoid misprints . referring to fig1 and 2 , the form factor for the roll of netstamps ™ labels 10 a and 10 b , respectively , will consist of a plurality of two part sets 12 a , 12 b , etc . on a carrier 14 . ( a portion of roll is shown .) the first part 16 of each set has a unique serial number 18 printed thereon in one orientation , e . g ., a horizontal orientation ( perpendicular to the long axis “ l ” of roll .) a second part 20 of each set comprises a releasable label borne on carrier 14 and if desired can have the same appearance of a netstamps ™ style of label that will be printed on sheets of labels , or can be different . the second part bears the same unique serial number 22 as appears on first part 18 , but typically is placed in another orientation , e . g ., in a vertical orientation along the long axis “ l ” of roll . in addition , second part 20 can optionally be pre - printed with a thermalchromatic printed logo element 24 , a facing mark 26 , and possibly also a line of microprinting 28 . a plurality of two part sets 12 a , 12 b , etc ., may appear on carrier 14 spaced apart by distance “ d ” ( see fig1 ), or sets 12 a , 12 b , etc . can be placed directly next to each other without any appreciable spacing , as shown in fig2 . first part 16 can comprise a separate label portion that is borne on carrier 14 . referring to fig3 , the roll of netstamps ™ labels 10 c can comprise a region 30 of carrier 14 upon which is directly printed unique serial number 18 , without the presence of a bona fide removable label . in this case , there is a single removable label with a unique serial number , but the unique serial number 18 is still visible to the user prior to printing the single label with postage indicia . referring to fig4 , there is shown a perspective view of an exemplary roll label printer 40 with first part 16 of a two part set on carrier 14 extending therefrom to reveal its serial number 18 . this is the position that the first label to be printed in a print run will have so that the user can verify that the serial number shown in the software matches the serial number of the first to be printed label . second part 20 ( not shown ) of a label set can be totally or partially concealed within roll label printer 40 and be ready for printing with postage indicia . fig5 is a perspective view of exemplary roll label printer 40 with one label set 12 fed out of roll label printer 40 after second part 20 has been printed with postage indicia and other information . as can be seen , after printing , first and second parts 16 and 20 of a two part label set 12 will extend from the roll label printer 40 . after printing , second part 20 will be printed with the 2 - d bar code 50 that encodes the postage value and type , sender information and the serial number , and in human readable form , the postage value and postage class 52 , the sender &# 39 ; s zip code 54 , and other sender information code 56 , which is better shown in fig6 . in the case that multiple labels were printed , then multiple sets of labels would extend from the label printer ( not shown .) referring to fig7 , there is shown an exemplary flow chart showing one possible embodiment of the system of the invention . in use of the system , first part will be feed out of a roll printer for serial number verification purposes prior to printing of second part with postage indicia . one exemplary embodiment of the serial number verification process is as follows . the program is first started 60 . the software displays a physical serial number to the user in a dialog , and the user is asked to hit a “ print ” button 62 . upon hitting the “ print ” button 62 , if the physical serial number that was entered in a dialog box indicates that the user is printing to a roll of labels in the label printer , then the software will send a command to the roll label printer to feed , or “ bump out ” the label set by a predetermined amount 64 . most roll printers support a skip command that can be used to advance a label a specified number of lines . this is done to a sufficient degree to reveal at least enough of the first part of the label set ( e . g . 1 . 6 cm ( ⅝ ″) so that its horizontally positioned serial number 18 can be viewed by the user even though the second part 20 of the label set is positioned for printing . the software will display a physical serial number 32 to the user . this can be done on screen , such as with an exemplary dialog box 34 as shown in fig9 and in step 66 of fig7 . within the dialog box 34 , the user is queried whether the serial number on the first part of the label matches the serial number displayed in dialog box 68 . if it does not , then user is given the option to either correct the serial number in the software to match what is shown in the display box to verify that the displayed serial number matches the number in the software 70 , or to cancel the print step , in which case the user can be taken back to a main dialog box 62 . if the serial number on the first part of the label matches the serial number displayed in dialog box 68 , the software will send a message to the roll label printer to print the specified serial number and label number , if no additional error handling is required 72 . as noted above , it is essential that the serial number ( s ) on the label ( s ) being printed match what the computer software is directing the printer to print on each label , otherwise the labels printed with postage indicia will be invalid . the system allows a user to print more than one postage indicia label at a time , e . g . 2 to 25 postage indicia stamps with first class postage . the system provides error control mechanisms that will help prevent a user from making common mistakes . see fig8 . for example , the system can help prevent a user from entering an invalid serial number into the software , and can display a message such as “ nnnnnnnnn . nnn is an invalid serial number . please confirm and try again ” 80 . another error control can be that if a user attempts to print more postage indicia stamps than there are blank labels remaining on the roll of labels loaded in the roll printer , the software will warn the user of this fact . for example , if the user increments the label number to a point where there will not be enough labels to print the requested number of labels , i . e . the user requests printing 50 labels on a 250 roll , but changed the starting label number to 240 on this dialog , the system can display a warning dialog , such as “ you have specified to print xx labels , but there are only yy available labels remaining on this roll . click ‘ ok ’ to print only the available yy labels , or ‘ cancel ’ to cancel this print job ” 84 . if the user ever cancels ( after the point where the serial number label has been bumped out of the printer ), the labels must be set back to tof ( top of form ) by sending a form feed command . in this case , after sending the form feed message , the label number ( which is stored as the default for the next print job ) must be incremented 88 . turning now to fig1 , there is shown a top plan view of another exemplary embodiment of a roll of postage indicia labels 100 . the roll comprises a plurality of label sets 102 a , 102 b , etc . on a carrier 104 . ( a portion of a roll is shown .) each label set consists of a leader portion 106 and a releasable main body portion 108 . the main body portions 108 can have the appearance and features of netstamps ™ postage indicia labels . if desired , the leader portion 106 can be divided into a serial number bearing portion 106 a and a supplemental information bearing portion 106 b ( e . g . which supplemental information bearing portion 106 b can be printed with information such as a sender &# 39 ; s return address so that it may be used as a return address label .) the serial number bearing portion 106 a can be made to be narrower than the supplemental information bearing portion 106 b . by providing the leader portion 106 in two parts , a user can use just the supplemental information bearing portion 106 b without including the serial number bearing portion 106 a . as with other above described embodiment of the roll label sets , a unique serial number 110 is pre - printed on leader portion 106 in a horizontal orientation relative to the long axis l of the roll of roll label set and the same unique serial number 112 is pre - printed on the main body portion 108 of the same label set . however , in the case of netstamp ™ types of postage indicia labels 108 , they are arranged on the roll with their unique serial numbers 112 aligned horizontally in the same horizontal orientation as the corresponding serial numbers 110 of the leader portions 106 . an advantage for arranging the main body portion 108 this way is that since netstamp ™ types of postage indicia labels 108 are typically not square and are taller than they are wide , this arrangement can accommodate a wider leader portion 106 which in turn can better serve as a return label . the main body portion 108 can optionally be pre - printed with a thermalchromatic printed logo element 114 , a facing mark 116 , and possibly also a line of microprinting 118 . as with the other embodiments of the system , the systems using roll label printers with built in ocr and / or bar code scanners described above can be used to print a single postage indicia label , or a range of labels that a user wishes to print . while the invention has been primarily described with reference to postage indicia label sets and methods of using these label sets , these rolls and systems can be used for printing other value bearing indicia , such as tickets , coupons and traveler &# 39 ; s checks , to name just a few . in these cases , rather than the labels being carried on a carrier , the items being printed may form part of the roll . having thus described exemplary embodiments of the present invention , it should be understood by those skilled in the art that the above disclosures are exemplary only and that various other alternatives , adaptations and modifications may be made within the scope of the present invention . the presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive .