Space Police: There isn’t any overall police service for the Associated Worlds – the closest thing is probably Conclave Security, which does answer directly to the Conclave of Galactic Polities, but whose jurisdiction is limited to just the Conclave Drift itself and its containing star system, and possibly the Operatives of the Presidium, who wield this kind of authority as one-off special agents.
In practice, every polity polices its own space, colonies, and the routes in between. The Great Powers often augment this with various roving fleets, asserting universal jurisdiction over assorted free-space crimes (piracy and such, usually), providing a kind of rough-and-ready frontier law and order. The loose structure of the Accord on Uniform Security provides for limited extradition and limited cooperation between polities (and Warden-Bastion PPLs), provided that hostilities aren’t, that everyone agrees that whatever happened was in fact some sort of crime, and that everyone’s having a reasonably nice day.
Within polities, of course, situations and law enforcement structures vary. The Empire, for example, doesn’t have a specific organization devoted to policing space. In planetary orbit, or among clusters of drifts, the Watch Constabulary has the same jurisdiction it does planetside or within habitats, and in Imperial in-system space, the same as its rangers do in the wilderness – the specialized divisions which operate “outside” are called the Orbit Guard and the Stellar Guard, but functionally, they do not differ from the norm. Major crimes in in-system space are handled by the Imperial Navy, but that’s functionally no different from the way that the Imperial Military Service planetside has generally been called upon to address riot, insurrection, and brigandage.
(In deep space, law enforcement is also provided by specialist units of the IN, simply because they’re the ones who can get there – and it’s outside all traditional borders anyway. And, of course, this excludes all private-conlegial/PPL bodies…)