I've created theorem-provers tag - I think we had a few questions about them. (IIRC we had coq tag, but it was deleted. But my memory might be fooling me.)

At cstheory they've used proof-assistants as the name of the tag.

I am not sure, which of the two possibilities is better. But if somebody wants to have the tag called (proof-asistants), we can make a sysnonym.