The flip side of this is that my son and I went to Dortmund on the ferry a few years back (also in a big BMW) and on the way out they properly searched the car like they thought we were drug dealers. So on the way back I said to my son, "wear your City scarf so they know we've been to the match, I don't fancy having the car fucked about with again." They stopped us for about an hour solely because he had that scarf on, at first refusing to issue us with a boarding pass then making us go into some kind of meeting in an office in the port at Rotterdam, threatening not to let us on the boat and saying that if there was any sign of trouble we'd be arrested. The whole thing was utterly bizarre.