Section 174.23 - Form of number(a) Each number must consist of two capital letters denoting the State of the issuing authority, as specified in Appendix A of Part 173 of this chapter, followed by- (1) Not more than four numerals followed by not more than two capital letters (example: NH 1234 BD); or(2) Not more than three numerals followed by not more than three capital letters (example: WN 567 EFG).(b) A number suffix must not include the letters "I", "O", or "Q," which may be mistaken for numerals.