When I brought our new Sovereign
from Germany to Austria, the Austrian police did not really like, that a car with an austrian licence plate tows a trailer with a german plate. And although Germany and Austria are in the European Union, this still is not legal. So I had to pay the small police fee of 21 Euro (equals around 21 US Dollars) and was allowed to travel home ... Here is the documentation of this nice case. It was nice indeed, because if the policeman would have insisted he could forbid me to travel further and try to get other licence plates, which would take several days and a lot of troubles and time. But the policeman was really impressed by such an "unusual trailer" which was good for me.