Prison has no cops. If you are talking about a guard, well there are none. Anyway. There are four ranks before you get the 'Free' rank. once you can get this rank you can go to the free world, and you a free to make a faction and a base. So. Prison is prison and factions in one.
Prison used to have guards that could jail people for a certain length of time. As I understand due to players 'abusing' this guards got removed from prison, and there will most likely never be re-added.
I was mistaken. I didn't play prison a lot when it first came out. I stuck to factions, infection and pvpfest.