Lesser vampiric trait.

[Katzen]

Maybe characters with this trait are vampires who work for NT and have willingly undergone a procedure of some kind to restrict their ability to keep them non-threats so they can count as human and keep their job. 

I know "who can work for NT" is a bit arbitary at this point with all the strange traits and races in the game even before character backstory but we are pretty consistent that we don't like reformed or "nice" antags conceptually. I don't remember us policing it as RP backgrounds but I doubt anything other than jailbird will ever get added as a feature.