If you are < 30 then it's not racism. It's profiling. The fact of the matter is that most young foreigners in Tokyo are complete hooligans. They're there because their families are on business or in the military. They freely roam one of the world's largest cities with almost no fear of the police. And, yes, they steal bikes with impunity, amongst other things.

Even if you do get stopped for genuine wrong-doing, the worst that happens is you get a talking to or a citation at the nearest kōban. Better yet, if you learn even the tiniest bit of Japanese that will generally set the policeman at ease.