Private vehicle numbers started in the mid-1900s when Singapore was one of the four Straits Settlements, with a solitary prefix S for signifying Singapore, then, at that point, adding a suffix letter S ‘B’ to S ‘Y’ for vehicles, however avoiding a couple of like S ‘A’ (held for bikes), S ‘H’ and S ‘Z’ (saved for taxicabs and transports), S ‘D’ (saved for municipal vehicles), and S ‘G’ for small and large vehicles. There was no checksum letter, for instance, S. At the point when the checksum letter was executed, these plate numbers were given checksum letters too, for instance, SG5999 became SG5999Z.

At the point when ‘S’ was depleted at SY, in January 1972, private vehicles began with E and Land Transport Authority started to make separate vehicle classes concurring kind of vehicles which already all vehicles in Singapore should bear prefix S because of past normalization with Peninsular Malaysia as indicated by topographical area (An is for Perak, B is for Selangor, S is intended for Singapore/Sabah), motorbikes with An and merchandise vehicles under 3 tons with Y. E was trailed by EA, EB with the letters EC in 1973 up to EZ. E was picked then as letters A-D were at that point in utilized by different states in Malaysia.[3] From 1984, the “S” series of number plates were dispatched again after EZ, however presently with two sequential postfix letters, beginning from SBA, despite the fact that with a few prefixes being skipped as they are saved, like SBS and SMB, as they were utilized for transports that have a place with public vehicle administrators. Anyway, under the Bus Contracting Model which was subsequently carried out, transport administrators under Bus Contracting Model use the SG prefix for every open transport.

Reference: Wikipedia

Series	Vehicle class
A_	Motorcycles until mid-1980s
CB	Company or school buses (discontinued in 1996)[6]
E_	Private vehicles from the early 1970s until the mid 1980s
F_ FB_	Motorcycles (e.g., FA–FZ); used till late 2005. Second generation prefixes (e.g., FBA, FBB, and so on); started at the end of December 2005. The current prefix being issued is FBS.
G_ GB_	Light Goods vehicles (class 3) (e.g., GA – GZ) till late 2006. Second generation prefixes (e.g., GBA onwards; introduced at the end of December 2006, after GZ. The current prefix being issued is GBL.
P_	Private operator buses (PA, PC, PD, PH, PZ were used to separate private buses, and so on, but later on all private hire buses were issued plates with PA, PC and so on). The current prefix being issued is PD.
Q_ _	Once issued to company-registered vehicles. Expenses incurred in the use of these cars were tax-deductible, though the road tax payable was twice that of a private car.[7] After a tax rationalisation in 1998 which did away with these benefits, company cars have been issued with standard number plates ever since.[8] The Q-prefix was used both standalone (e.g. QB 1 K) and as a prefix for, E, B and C-series plates (e.g. QEZ 6257 R, QBX 2223 K, QCK 6861 Z)[9]
S_ _	Private vehicles, also formal number plate series. The current prefix being issued is SNC. Older vintage series with two letter prefixes conflict with some Sabah series.
SH_	Taxis or street hire vehicles such as Singapore-Johore Express, former SBS buses operating Sentosa and Airport services (AIRBUS) and Singapore Explorer Trolley – City Sightseeing buses. The current prefix being issued is SHF.SH was also previously used for public buses that were not operated by the Singapore Traction Company (e.g. buses under the Chinese bus companies and later, SBS from the 1960s to 1974, when new SBS numbers were issued specifically for SBS buses.)
TR_	Trailers. The current prefix being issued is TRD.
W_	Engineering plant vehicles (Class 5), some registered Jeeps and Rovers. The current prefix being issued is WD.
X_	Very heavy goods vehicles (Class 5/prime movers) not constructed to carry any load. The current prefix being issued is XE.
Y	Heavy goods vehicles (class 3/4) which are constructed to carry load or passengers only. The current prefix being issued is YQ.
12345	Power-Assisted Bicycle (PAB) number plate with a maximum of 5 digits. Registration is mandatory in order to be used.

Other specific vehicle types

• CSS: City Shuttle Service buses (no longer issued: some re-registered under TIB series while the rest were deregistered.)
• LTA: Land Transport Authority enforcement officers’ vehicles.
• MID: Singapore Armed Forces vehicles (this is a suffix with up to five digits before it, e.g., “12345 MID”). “MID” originally stood for the Ministry of Interior and Defence. General ranks in the armed forces are provided with staff cars with two-digit MID plates.
• MP: Vehicles operated by the Singapore Armed Forces Military Police Command. (SAFPU plates were formerly used)
• NZ: Vehicles of New Zealand diplomats and Installations Auxiliary Police Force (ANZUK).
• PU: Tax-exempt, restricted for exclusive use with permission on the island of Pulau Ubin
• QX: Emergency and law enforcement agencies (Singapore Police Force, Singapore Civil Defence Force, Immigration and Checkpoints Authority, etc.)
• QY: Quasi-government agencies and statutory boards
• RD: Research and development vehicles (such as electric, fuel-cell and smart car rental vehicles).
• RU: Restricted Use vehicles, a special category for vehicles for which road taxes are not paid. A vehicle with such a licence is restricted for use within certain areas, for example a pushback truck within the grounds of Singapore Changi Airport or shuttle buses on Sentosa island and other southern islands of Singapore. When travelling out of the restricted boundaries, such vehicles are either required to be tagged with a trade-plate or towed.
• S/CC: Vehicles of the Consular Corps
• S/CD: Vehicles of the Diplomatic Corps
• S/TE: “Technical employment” vehicles
• S1 to S10: State cars used for ferrying official government guests and dignitaries
• SBS: Buses operated by SBS Transit (from 1973) until Jan 2016. Currently also used by Tower Transit and Go-Ahead Singapore.
• SDC: Buses operated by Sentosa Development Corporation (No longer issued, replaced by RU plates)
• SEP: “Singapore Elected President” – the official state car of the President of the Republic of Singapore (SEP 1)
• SG: Government-owned buses operated by contracted bus operators under Bus Contracting Model. Formerly assigned to goods vehicles, most goods vehicles were de-registered by 1998.
• SJ: Supreme Court judges (the Chief Justice‘s car has the plate number “SJ 1”).
• SMB: Buses operated by SMRT Buses until Jan 2016, used in tandem with the TIB series. Used for buses registered after the merger of TIBS and SMRT in 2004. Currently also used by Tower Transit and SBS Transit.
• SP: Speaker of Parliament (SP 1)
• SPF: Commissioner of Police, Singapore Police Force (SPF 1)
• STC: Buses operated by Singapore Traction Company. (All deregistered, operations ceased since 1971).
• SZ/SZA: Older rental vehicles and chauffeur-driven private hire cars. Since the car tax rationalisation of 1998, private hire and rental cars have been issued with standard passenger vehicle prefixes.^[8] Currently SZ prefixes are used on private boats/yachts with (a suffix with up to five digits after it with checksum).
• TIB: Buses operated by SMRT Buses registered prior to the merger of Trans-Island Bus Services (TIBS) and SMRT from 1983 to 2004. The last of these buses were deregistered in January 2021.
• TP: Motorcycles of the Traffic Police Department, Singapore Police Force.
• LM: Lifting machines such as crane. i.e. (LM123456A) issued by the Ministry of Manpower.
• C: Construction equipment i.e.(C12ABC).

Special prefixes were used for specific events, such as:

• ASN: Vehicles used by VIPs and delegates during the ASEAN Summit held in Singapore in November 2018
• WTO: Vehicles used during the World Trade Organization‘s inaugural Ministerial Conference held in Singapore in December 1996
• IOC: Vehicles used during the International Olympic Committee‘s 117th Session held in Singapore in July 2005
• NDP: Vehicles used during the National Day Parade, 2005, on 9 August 2005
• AIRSHOW: Vehicles used during Singapore Airshow
• APEC: Vehicles used during the APEC Annual Meetings in November 2009.
• SIWW: Vehicles used during Singapore International Water Week
• WCS: Vehicles used during World Cities Summit
• YOG: Vehicles used during the 2010 Summer Youth Olympics.
• SEAG: Vehicles used during the 2015 Southeast Asian Games.
• APG: Vehicles used during the 2015 ASEAN Para Games.
• HSBC: Vehicles used during the events organised by HSBC (Hongkong and Shanghai Banking Corporation)
• OCBC: Vehicles used by OCBC during annual cycling event. Such as OCBC Cycle yearly
• SGP (without checksum suffix): Vehicles used during the Singapore Grand Prix.^[10]
• IMDEX: Vehicles used during the 2017 Maritime Defence Exhibition & Conference (IMDEX Asia 2017)
• CESS: Vehicles used during the CleanEnviro Summit.
• IW: Vehicles used during the Interpol World.