and the uniforms are also relatively easy to duplicate, get a duty belt to add to the set-up with a glock and you'll be assumed to be a cop. and if you want to go all out buy a used crown Victoria with the police rims and paint it up like a unmarked police car
Which explains why cartel members operating on our side of the border like to impersonate police when carrying out hits/robberies these days... who's to say that some people are police or not? And with how kind police departments are these days, "Oh, you didn't believe him when he shouted 'Police'? Just because it was night and he was in normal clothing? Too bad, prison time."