A classic article from the 1990s for the ORB by none other than Andy Chambers. It is not a long article, yet it contains good background information on the Adeptus Arbites, their job of Imperial law enforcement, and ideas about how they can function in your games.
Remember, the Enforcers enforce Helmawr's Law and the Arbites enforce Imperial Law.
These are the rules for the Adeptus Arbites, the harder older brother of the Enforcers. They are fun rules, though these guys are pretty tough. They don't take ammo rolls, they have boltguns and grenade launchers and the awesome Executioner rounds for their shotguns. Has some great colour photos of the paint scheme and some nice terrain shots too.