Black Hand is not a title, it is a trait unrelated to any sect. The trait is not lost if the vampire changes sect.
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Sennadurek
G4Sabbat. Black Hand: Whenever a Methuselah loses the Edge when it is not your turn, Sennadurek unlocks, and you may look at that Methuselah's hand. Scarce.
Rulings
The scarce penalty considers the apparent clan while controlled (in case of Clan Impersonation and Banishment).