The Faceless playbook of Apocalypse World (both 1e and 2e limited playbooks) states the following:
The Unexpected: when someone sees you unmasked for the first time, they take s-harm, in addition to anything else that happens.
Does that apply only to the moment of unmasking, or seeing the Faceless without the mask in general? I think the former makes more sense in the narrative, but feel the latter is a more natural interpretation of the wording.