"And he causeth all, both small and great, rich and poor, free and bond, to receive a MARK in their right hand, or in their foreheads: And that no man might buy or sell, save he that had the MARK, or the name of the beast, or the number of his name. Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six."
Often referred to as the "Devil's marks" by mundane inhabitants of the Dark Medieval world, these anatomical aberrations sometimes manifest on those who spend too much time consorting with demoniac powers. Certain mortals or vampire who have entered into bargains with the infernal or have otherwise kept company with the denizens of the nether realms may also display these physical anomalies. Possible deformities include, but are not limited to: malformed teeth, club feet, a horrid stench, slimy excretions, tough or warty hide, parasitic infection, putrescence, vestigial wings, or other ineffectual limbs.
—Vampire: The Masquerade - Clanbook: Baali