It is not illegal to violate the rules, but this is generally ignored. Just don't show off. When I was in the police academy, I once didn't change my police uniform for the convenience of going home, so I was unlucky enough to be picketed. I asked for my student id card, but I didn't bring it, and I didn't call the school to confirm it. Generally speaking, as long as you are not unlucky, you will be fine, provided that you don't really pretend to be a special police officer or a policeman. That's illegal, or your clothes will be confiscated at most.