I was on a thread in RPG.net asking about potential names to use for "The Agency" the PCs belong to in this draft campaign, and I ended up getting a few good questions that got me thinking more about the game. The good thing about good questions is that it finds you reexamining your assumptions and you end up with a better idea of what you are doing.
Q: I would start off by working out when and where this organization was created. Is it something crafted centuries ago, or did it only come into existance in modern times, when fast communication and travel means that enough monsters can be in contact at once to form an effective police force?
Me: I think that there has always been a few supernaturals who took it upon themselves to police the excesses of other local supernaturals, this activity didn't exist as an hierarchical organization or agency. It was probably born in the modern era, given the dangers of quick communication, information retreival and global travel. While those factors would help an agency function, it would do wonders for mortal hunters and also enflame local mobs to be a much larger and more difficult to manage scale. The fear would be that in the past the local village would flip out and kill the local supernaturals, but now these mobs could engulf entire regions - if not entire nations.
This would also create a nice rift between the needs of the supernaturals to keep the "masqerade" intact along with the powerful "old school" monsters/wizards who don't like young turks policing them or telling them what to do.
Q: Is it purely a police agency, or do they have the power to carry out trials and pass sentences?
Me: I'm envisioning that supernatural "society" is best described as anarchy. There is no law, conventions, or constitution, although supernaturals are definately aware of and interact with other types. (A cabal of witches can hook up with a werewolf for a bit of security muscle). What "The Agency" has is the consent of many weaker supernaturals who are acutely aware of the danger that mortal hunters present, and thus tolerate "The Agency" having a group of troubleshooters not only putting a lid on the problem, but providing services to said supernaturals. ("Vince the Vampire lost his blood bank access due to tight security and record keeping and now Vince is reduced to assaulting mortals in dark alleys. If the PCs help him get a stable herd, the risk of hunters detecting the supernatural drops, and it gets Vince indebted to the Agency when they need his services to figure out how to deal with the crazy elder vampire, Baron Belial and his brood.")
So, they have the power to carry out trials and pass sentences, so long as they can convince others that what they are doing is in their best interest. As a result, I'm planning that there will be supernatural antagonists in the game will try to frame "The Agency" as the tool of other elders to seek out and destroy their enemies. (Baron Belial might realize that the Agency is a threat to his power, and thus could try removing that threat...)
Q: Do agents join for life, or are most of its operatives volunteers for a limited term of service?
Me: I'm envisioning that it's largely a volunteer force, however there are some that are roped into it for life. If you are a supernatural who is somehow dependant on your master for some reason, and he supports "The Agency", he could probably easily compel you into a lifetime of service.
The majority of supernaturals who join do it because of personal reasons and because they believe in the cause. Kinda like why people become police officers.
Q: Based on [my responses above], it seems like the organization is going to have a very decentralized, informal structure. They are probably less organized than the Boy Scouts, much less the FBI. Actually, the organizational structure of the Boy Scouts would probably be a weirdly appropriate starting place. That is, there's a national organization that sets standards and gives approval for individual "Troops" to call themselves Scouts, tracks membership records, and organizes national events. Yet at the same time, the national organization has little say in the day-to-day operation of an indvidual Troop, which must secure its own meeting area and (generally) fund and organize its own activities. The national organization is only likely to intervene if there is some complaint that the local Troop is in some way not living up to Scout standards.
Me: "The Agency" is structured that way because while I want a police-style game, I really don't want a heirarchy that tells the PCs what to do. I don't want Bureaucracy: the Procedural. I want the characters to be the primary drivers of the local law enforcement community, and not a precinct captian telling them what to do. The PCs will be largely responsible for handling the day to day affairs of their "turf" and insuring that their broad mandate for maintaining the veil of secrecy is their responsibility #1. The PC's superiors will give them broad marching orders, access to resources (information, guns, money, safehouses, etc.), and the requirement to regularly report on their activities. In fact, if their superiors show up, it's either to help out with something near the end of some investigation (such as to incarcerate someone) or because the PCs screwed up bigtime.
Q: Have them operate according to a "Night Watch Handbook" that lays down the operating principles and rules of the organization, with some handy operational pointers. Each Watch is probably organized on a town or metropolitan area basis. Each Watch is responsible for getting funding and support from the local community and sending dues to the national office. (It's funded from the bottom up, not the top down.) More than anything else, the whole thing is held together by a common reputation. People trust the Watch because it's been effective elsewhere.
Food for thought!