One of my best friends has a uniform fetish, and he's sent me pics of himself done up in various ones. From security guard, to cop, to baseball player, to military grunt. It also helps that he's one hot SOB who is now an avid gym person. He doesn't need to be in an uniform for me to want him, but every pic just makes me want him more.
I've never fooled around with a cop, but a couple of times I've managed to have a quick session with a security guard. One of the hottest was back in my hometown when I was younger. I wound up hooking up with a guard who worked for public transportation. He took me to the station's locker room, hid behind some secluded lockers and whipped out his "nightstick" for a spit shine. I couldn't reject such an offer! We almost got caught, which I think added to the rush. Not that I'm all into having sex in dangerous spots, but the fact that it happened so randomly is quite interesting.