The idea is a fairly simple one. A registry is kept and maintained - likely by the guard faction - of those in or around the Vallaki area.
Perhaps my perspective has been somewhat squeued by playing mainly within a secretive faction, but it often seems as if Vallaki is overrun with wandering vagrants. People that really have no ties to the city in any way, shape, or form, and as such are completely under the radar when it comes to recognition on a grand scale. A registry would allow the guards to have an official record of all those that wander around the city, and could also grant those on the registry some benefit as well. I wouldn't suggest any scripted penalty for not being registered, as oppressive systems rarely are fun, but rather make it a choice that people want to make, if just to avoid the Guard's ire and suspicion.
Thoughts/deas/feedback/suggestions?