Why do vampires cover there faces with their cape?

In older forms of vampire mythology, the vampire did not reside among humans but lived in a castle out of the way (only coming to the towns to feed). Part of this tradition was that vampires were much more noticeably non-Human than modern Twilight-esque vampires. Specifically, their fangs did not withdraw when they were not feeding, so in order to hide their identity from potential prey, they would use their capes to cover their mouths.