License plates for private cars started with a single prefix 'S'.
With the growing car population, there is a need to increase a suffix letter after the 'S', and thereafter it was imposed to two serial suffix letters, starting from 'SBA'.
Exceptions of certain prefixes:
SH - Taxi
SBS - Buses operated by SBS Transit
S, ending with CD - Embassy
TP - Bikes operated by Traffic Police
PA, PB, PC, PH, PZ - Private hire vehicles
LTA - Bikes operated by Enforcement Department
To prevent forming words that may lead to objectionable opinions, the Land Transport Authority has skipped the use of vowels in the second letter of the three-letter suffix. For example, when the sequence of 'SDZ' ended, the 'SE' series was skipped and it continued with 'SFA' instead.