Figured I'd post this question here since others might be wondering as well 
Ouro and I are noodling over a pair of Tower police offers/detectives. How similar do Tower police function to real life police? Are they the same/separate? Should PC police peeps have a specific department they work (like vice or homicide or etc etc) or should their jobs be more generalized and flexible so they're available for more plotlines and interaction opportunities?
Tower police are "the police" in cities that have a Tower, towns than have a Tower auxiliary office, etc. They're made up of both Sentinel and Normals, though particularly in Tower cities there's an obvious preference in promotions etc. for Sentinel. (Normal police officers wouldn't be out of place for resenting that.

) Technically, there are also state police and federal officers (e.g. FBI) who are not Tower. Jurisdictional grey areas are frequent. America!
There are departments within the Tower police, specifically: Arson, Counter-Resistance (go after violent resistance groups, e.g. Chainbreakers), Homicide, Hunting (look for rogue Guides), Theft (includes burglary, auto theft, etc.), Vice (focused primarily on drug running), and White Collar Crime. All beat cops and detectives have generalized training in everything
except White Collar Crime and Arson. Generally speaking, newbies will spend the first two or three years drifting between departments until they show promise in one area. (Or get kicked out whoops.)
PC cops, unless they're top level types, should have a department they answer to. As a GM suggestion, I would point to Counter-Resistance, Homicide, Hunting, and Vice as choice spots to get in on the action. However, choosing another department won't necessarily mean you're cut out of doing police-y stuff. There will be events happening that will, ahem, "require inter-departmental cooperation".