I think everyone feels this way at some point about their own nationality. Everytime on the tube I thought I've spotted an American or Candian, I've been right (yes I skulk behind to hear them talk!) and am annoyed that they are so obvious. Even two people who were dressed well (she in a cognac leather jacket) seemed american from their hair and the fact that the jacket looked like Mike & Chris. I think when you're from an area you just have an innate sense of others who are also from there. Everyone when they see my boyfriend say 'he looks SO british' so I mean, there are obviously certain looks which are typified and cross national boundaries, if this makes sense.