Private car licence plate numbers began in the early 1900s when Singapore was one of the four Straits Settlements, with a single prefix S for denoting Singapore, then adding a suffix letter S 'B' to S 'Y' for cars, but skipping a few like S 'A' (reserved for motorcycles), S 'H' and S 'Z' (reserved for taxis and buses), S 'D' (reserved for municipal vehicles), and S 'G' for goods vehicles large and small. There was no checksum letter, for example, S. When the checksum letter was implemented, these plate numbers were given checksum letters as well, for example SN9889 became SN9889U.