Are you good with riddles?

give me a x (as in times sign) and i'll stand and face you
give me a + and i'll turn away from you
what am i?

hint:
russell crowe is obsessed w/ this in a beautiful mind.

a negative?

A negative number?
Example.
-2x2=-4 so it turns to face the negatives, but if
-2=2=0 so it turns away from negatives.