I made a wooden stamp by carving with a dremel, and use that somewhere on my pieces. It's a celtic spiral design that resembles a raven. It's big, though, and tends to deform my work if I'm not careful, so I need to figure out how to make a smaller one. I'll probably carve one from clay, even though carving clay tends to piss me off.
I don't like to sign my pots. I'm not entirely sure why. I always get the feeling I'm "doing it wrong" which is really stupid, I know. Writing my name on the bottom feels weird, and I think my signature looks too plain anyway. So far, the only pieces that get marked consistently are mugs, because I stamp into the fishtail join on the handle...which, incidentally, looks pretty dang cool.