Thanks! I must admit this is the first time I have heard of the acronym.

Based on https://en.wikipedia.org/wiki/International_vehicle_registra...

D, A and CH are the international vehicle registration codes for those countries among other things. and "dach" as a word means "roof", which makes it memorable. some more fun facts here: https://en.wikipedia.org/wiki/Geographical_distribution_of_G...