The Rostock Hansenstadt is the flag for a German City. The colors come from the arms and so does the dragon.
Rostock (/ˈrɒstɒk/ ROST-ok, German: [ˈʁɔstɔk] (listen)), officially the Hanseatic and University City of Rostock (German: Hanse- und Universitätsstadt Rostock), is the largest city in the German state of Mecklenburg-Western Pomerania and lies in the Mecklenburgian part of the state, close to the border with Pomerania.[a] With around 208,000 inhabitants, it is the third largest city on the German Baltic coast after Kiel and Lübeck, the eighth largest city in the area of former East Germany, as well as the 39th largest city of Germany. Rostock was the largest coastal and most important port city in East Germany.