What do crucifixes do to vampires?

Nothing.
The thing about crucifixes and vampires come from a particular quirk of Count Dracula. He was a christian soldier while he was alive and apparently a rather devote one. Vampires retain the personalities they had while they were living and are rather incapable of (significant) change after they are dead. So Dracula (and he alone) was adversely affected by the sight of anything suggestive of religion. He had a hard time resolving his old life with his new 'life'.
As he was a particularly famous vampire his traits have been applied to all vampires.

other quirks the Dracula had that may not be applicable to other vampires

1. Could not actively cross moving water.
2. Had to be invited into a place.