I was washing my car and saw a guy walk passed me, looking lost, did the awkward look at him, and he asked me for directions to a house, I tried to help him, but I had thought his accent sounded a bit American, but just left it at that... He then walked passed me a little later and I asked him if he found it, and I told him "You sound a bit American" he said "I am.. from Arkansas, been here 10 years now"
Another time when I was living in London, I was working at a Co-op (first UK job) a girl came in dressed as a cheerleader, she sounded American, I asked her and she said, "I'm from the US", I said "So am I!" Her reply was "so, what? I don't care" haha!
Another time, at the antique store in Huntingdon, I heard a guy talking, asked him if he was American, he said yes, and he was stationed here.
I did make good acquaintances with a serviceman, we were at a bar, and my wife noticed a guy at the bar and said he looked American, so when I went to get our next drink I heard him talking and realised he was southern, asked him about where he was from, and he was an American stationed here, he bought me a few American things.. Ranch dressing, Taco Bell (Before they opened in the UK), Mt. Dew.... (I work with a woman that does all of her shopping at the base because her friend is American, makes me angry)
My wife ends up having to point out Americans for me... haha