Thanks guys! Actually, I was thinking of something presumably simpler. Lorentzian spacetimes have "time" or "times" that Riemannian spacetimes don't. In AdS/CFT, what in the boundary theory determines the signature of the bulk geometry?
Papers like http://arxiv.org/abs/0804.3972
seem to have Galilean boundary theories with Lorentzian bulk, so I presume it isn't the signature of the boundary that determines the bulk signature? (Or is this some weird thing that condensed matter folks do that "real" string theorists wouldn't contemplate?)