Hi David!!
On the subject of recognizing American tourists, I guess they can't really disguise. I grew up in a town with an American army base in Germany, and, looking at people in the streets, I could always tell who was American and who wasn't. It's not only the clothes, but also the way people move, their facial features, hairdos and glasses, how they laugh and look around. I can't really put my finger on it. It's their whole appearance. Once, a cousin from the United States who visited us wanted to try out his German vocabulary on a guy walking past our house, saying aloud "Guten Abend!". I told him, that was an American GI, and he asked how I knew. I couldn't really explain it. It was just so obvious. On the other hand, I also recognize German tourists anywhere...