Two years ago I was in Florence, Italy at what turned out to be the same weekend the Europeran Economic Social Forum had their big rally. One million people at the parade, very anti-war, there were deaths from the rioting at the same rally last year. The U.S. mid-term elections took place earlier that week (I was in Rome then, and the headline in the paper I read the next morning was "U.S. Chooses War", that was funny).
Anywhoo, back to the rally, the U.S. Consulate in Florence handed me a warning from the State Department that they were giving to tourists to not be in Florence that weekend. Hotels were boarding up their windows, riot police were on all the street corners, paramedic units were being set up all over the city.
What I'm getting at is this. I spent the whole weekend there, did the whole tourist thing with no problems whatsoever. I didn't have to "not speak", or hide, or sew a Canadian Flag on my clothes, or avoid people, or any of that crap.
There is a lot of conflicting stories being floated about when it comes to treatment of Americans in Europe. All I did was this, it's really simple. I Didn't act like a selfish prick, I didn't make a spectacle of myself and I tried to be respectful. Just like people should act every day, it's no different there than here.