Not at an airport. In August, on a train from Hamburg to Copenhagen, shortly after we crossed into Denmark, Danish police officers passed through the train asking for passports. I took my US passport out of the passport wallet. As soon as they saw the cover, from approximately a meter away, I was told that it was fine; I didn't even have to open the passport. It was the same for the two Germans in our compartment. They did, however, look through the passports of the Romanian couple who was sitting across from me.