A further safety element is constituted by the fact that said markings 10 are embedded in {HEAD ~ patterns} which constitute the normal safety printings or patterns, indicated by 20, so that said markings cannot be easily perceived optically since, although they are present, they constitute an integral part of the safety pattern or {TAIL ~ printing} 
A further safety element is constituted by the fact that said markings 10 are embedded in { HEAD ~ patterns } which constitute the normal safety printings or patterns , indicated by 20 , so that said markings can not be easily perceived optically since , although they are present , they constitute an integral part of the safety pattern or { TAIL ~ printing }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL