Apologies for a very basic question, but this is something that I always forget, and it's a pain to find with google and the like, so I'm putting it here for everyone's future reference.
As far as I recall, it's
$\times$ but that's not working in a
matplotlib plot title (perhaps because
matplotlib doesn't implement that particular symbol?).
I get something like "A
imes B" (with
imes in latex font) for the title "A $\times$ B".