Can I sign up more than one vampire?
As a general rule, no - if several vampires belonging to the same person act in concert (eg. attacking the same target, collecting money for use by one main vampire or pooling their resources in any other way, being sired by the same vampire), I may delete any number of them. That said, a couple of vampires acting fully independently is okay, and will go unnoticed. *Don't* have one sire the other (it's fairly obvious that that's cheating, yes? You can't get nutrition by draining your own blood!)
Making lots of vampires for a friend (or an enemy) is also disallowed; the blood they gain will be removed, and the player who creates the false-vampires risks their main vampire being deleted.