I'm like redBoobergurl; I change my sig depending on my whim. I've had a link to my Scooter fansite in my sig, I've had a quote from Doctor Who and I've had lyrics from a couple of my favorite musicals.
My current signature is the last line of an old joke or folktale. It's about a guy who has to teach a horse to sing, and the king gives him a year in which to do it. If he can't teach the horse to sing, the guy will be executed. When asked by a friend why he's bothering with this seemingly impossible task the guy replies, "A lot of things can happen in a year. The king could die, the horse could die, I could die. And who knows? Maybe the horse will learn to sing."
-Kim