At that time all the counties were discussing the three-letter/three-numeral number plate decision, he said. The thinking was that if a witness was able to say that the license plate of a suspect vehicle contained the letter H, K, M or L, regardless of whether the letter was in the first, second or third position, the search for the vehicle could be limited to those number plates beginning with those letters, Kamimura said.
Not only are the letters H, K, L and M not used in the beginning of a letter sequence for Honolulu number plates, they are not used, period, confirmed Dennis Kamimura, administrator of the city Motor Vehicle and Licensing Division. H, K, L and M are reserved for the neighbor island counties, while O, I and Q are not used because they are too similar to the numerals 1 and 0.
As to why H, K, L and M are not used at all, Kamimura said it was an administrative decision made in 1979 or 1980 to help police identify vehicles.

Jon Cherry is a Director of leading personalised number plate dealer Regplates.com. Jon has over 25 years industry experience handling some of the most expensive plates ever sold with many high profile and celebrity clients. Active since 1991 in the number plate industry, Jon is currently Chairman of the Cherished Numbers Guild, a trade body representing number plate dealers in the UK. Jon has written many articles on the industry and insight into the future of numberplates and the market as a whole.