Towns would have there own police that would have a specific uniform, and would walk around the area and make sure that mobs don't spawn in the city. Also to have an ability for Police to target griefers. Killing them would put them in a town jail. (They would lose all their stuff)

Hm, this sounds cool. I'll have a look through Citizens' API later.

The issues I mentioned on the Jail ticket still apply here, so making the sentries auto-jail griefers is out. However, making them akin to iron golems (in that they protect the town they're in from mobs) does sound like a cool idea. And just having them patrol around and say things would be nifty (I'm thinking vaguely of the Imperial Guards from Oblivion as I write this).

Maybe I'll integrate this with the town level-up feature I've been thinking about.

I'll tentatively assign this to the v2.3.0 milestone

The difference about the Citizens API, is it is legit Player NPCs as opposed to Iron Golems. Sentry (which is a character for Citizens) already has the logic and such for killing mobs, and players and other NPCs. The only thing that I think you would need to do is see if there is an API for Sentry. Also perhaps having more than one type of Police / Guard. For example SWAT, which would throw bombs instead of shooting arrows.

Closing this- I don't want to devote developer resources to this over other issues.