Hey, I actually have experience in this area! I once stole a forum out from under its original creator and Brand Manager, who, like Ali, wanted to keep the trademark to himself. His forum was "Perpetual Motion", so mine became "PM:X". And then I later passed it on myself, and it became "PM:X^2". How clever!
So, "RC:X" is the obvious choice. And then when Royal Crown comes out with their new "eXtrEEm" version of RC Cola, we can sue 'em.
Neil