#14:
Look, as you probably know better than me, this subject of "will people in Europe dislike me because they think I'm American?" comes up every once in a while. Sometimes the posters are just trolls who try to stir up an endless discussion between Europeans and Americans about Iraq, sometimes people are genuinely worried about how they might be treated if they are mistaken to be American. I'm quite confident that this OP is not a troll, so I decided to send a reply, and though it may have sounded a bit curt I absolutely did not intend to make a fool of OP.
This is an international forum, so unless an OP specifies that only replies from his/her countrymates are appreciated, chances are that some foreigner reacts. Dismissing the opinion of a local as worthless is IMHO quite rude, although I admit that first-hand experiences have higher value than comments from locals trying to put things in perspective.
Maybe it's because I'm from a small country (the Netherlands) and I'm used to being mistaken for an American (until my accent or English mistakes give me away, at least), a German (hey, that's the same anyway, right? - not trying to sound bitter but that is how people from small European countries are sometimes told) or even an Israeli (I look almost as northern European as possible), but I couldn't care less personally about being mistaken for some other national. This would be different if there would be a chance of getting stones thrown at me or being mobbed because locals think I'm an American, but AFAIK that has never ever happened in Europe in the past decades.
Of course there are people around who think Canada = USA or American = Bush supporter = totally wrong, but if you would adjust yourself to what locals might think of you, you'll have a hard time. It's also not like all Europeans are against Bush or don't see the difference between Americans and Canadians. Besides, loads of Americans travel around Europe, are they all met by hatred and anger from locals? And why would you care about narrow-minded people who won't help you because they think you're American? Walk two steps and you'll find someone else to give you directions.
On the other hand, locals you meet on the streets won't first check the flagpin on your backpack before they decide if they're going to help you finding your way or to sell you goods. Rushing into a small shop in Spain and launching off in English without considering if the shopkeeper will understand and then reacting in an annoyed way when you can't make yourself understood, is an (albeit exaggerated but not totally fictious) example of a good way to get a bad reception. That's why I stick to my previous remark in post 4.
You have clearly based your opinion on personal experiences and say you feel more comfortable with a flagpin. There is, as you point out, no way I can come up with a better argument against the flagpin, so I won't even try. I also like to make very clear that my remarks are only an attempt to offer the OP a perspective from the point of view of 1 individual person from 1 country in Europe and that I am absolutely not trying to win an argument against someone who is judging from his own experiences, as I fully respect your opinion.