Don't travel to Germany without this database of the German license plate signs. The letter code denotes the different regions. You can search for the code, the region, the cities and filter by countries.
The application helps you to collect all different codes. This is a famous game for kids during boring long car trips.
There is a quick link from the region and the country to Wikipedia to read more.
This application is in German, but can be used by anybody who travels through Germany or is curious about the German license plates.