Why would you hold up a cross? Wouldn't that be a Star of David, or a Torah, or some other such thing in your case?
Actually, the Richard Matheson book I Am Legend, upon which the Charlton Heston film The Omega Man was based, proposed exactly this sort of thing. Crosses only repelled vampires that used to be Christians, convicting them of the moral code that they once held. Stars of David (Star of Davids? How do you pluralise it?) worked on formerly Jewish vampires, and so on.
Logic would tell me it's "Stars of David," but then again logic tells me that it should be "teaspoonsful." ;-)
(Psst: There are no Jewish vampires. Vampires are a scam that Catholics came up with in order to get more movie gigs for priests. And good PR for Holy Water. )
SD