Our tour guide explained to us that the Hamburg license plates bear the letters "HH", which stand for "Hansestadt Hamburg", because Hamburg was a part of the mediaeval Hanseatic League (along with the cities of Bremen and Lübeck. All car licenses bear a code indicating what city they are registered in (licenses from Bremen and Lübeck start with "HB" and "HL", respectively).

However there is another anecdotal story behind the Hamburg license code. One of the folk tales of Hamburg talks about "Hummel Hummel" -- this was a bent old man who carried water in the town in the old times. He was always going back and forth bent with his load, busy like a bee. Local youths would tease him calling out "Hummel Hummel" (which is sort of an onomatopoeia for the sound of a bee). Supposedly he would get annoyed and respond (and I am not sure I am spelling this right) "Mors Mors", which is a kind of dirty phrase, like "Kiss my ..." Well this story has passed into local legend and become an object of levity, so supposedly if you say "Hummel Hummel" to any native Hamburger, he or she will respond with "Mors Mors". And that is the other explanation sometimes given for the code on Hamburg license plates -- it's short for "Hummel Hummel"!

And, by the way, the "D" on the left of the plate in the blue field with stars stands for "Deutschland" (Germany), and the blue with 12 stars is the symbol of the European Union.

Hamburg license plate