For many countries, the registration number begins with a obvious letter (F for France, D for German (Deutschland I guess), C for Canada,...). For other, historical reasons have already been covered here (e.g. Where did the US 'N' registration letter come from?).
But for Belgium, I find it weird to begin with OO. Is there an historical reason for that? if so, what is it?
D
is forDjermany
. Just say it aloud and suddenly it makes sense. ;-) $\endgroup$