The design for vehicle registration plates in EU countries was standardised in 2000, and since then they have had four numbers and three consonants, preceded by a white letter on a blue flag to identify each country (E for España, in the case of Spain).
In Spain, on 18 September 2000 a 1981 Mercedes-Benz 230 SL with a León number plate was the first to be given one of the new types of registration: 0000-BBB. Normally, the sequence would have begun with 0000-AAA, but the Directorate-General of Traffic (DGT) roads authority had decided not to use any vowels or the letters Q, CH, LL and Ñ on registration plates.
The reason? They wanted to avoid any unfortunate letter combinations such as PIS (meaning pee in English), ANO (anus), acronyms such as ONG (NGO) or PCE (Communist Party of Spain) and names such as EVA, ANE, and ANA.
The letters O, Q, Ñ, CH and LL in the Spanish alphabet were also excluded to avoid confusing them: the Ñ with an N, for example, or the Q with the O.
The alphanumeric code has no specific meaning; the registration number is just a way of keeping an official record of the vehicle and its owner(s).