From Longman Dictionary of Contemporary Englishregistration numberregiˈstration ˌnumber noun [countable] British EnglishTTC the official set of numbers and letters shown on the front and back of a vehicle on the number plate
Examples from the Corpus
registration number• For companies you need their full name, country of registration and registration number.• From its registration number it was only three years old, and it looked well-kept, the front tyres were new.• Some also alter the painted registration number on the car to match the fake plates.• If the stamped-in number is too hard to find, check the registration number against the excise licence.• The registration number of any vehicle seen swopping lanes was recorded and radioed ahead to the entrance where they were stopped.• In any case, it was the wrong registration number. 