The shape that gets left behind when you
burn yourself with a cheap
cigarette lighter. Not by holding the
flame up to your flesh, but by leaving the lighter lit for a couple minutes, and then pressing the wheels and the front part against your
skin for a while.
While some people might use this as a cheap alternative to getting a smiley-face tattoo, if you're only interested in minor self-mutilation, you might want to avoid touching the wheels to your skin, because it's pretty embarassing to see the end result of all your angst/depression/whatever offering you a great big grin every time you look at it. The only friend I showed my =) to laughs uncontrollably each time she sees it.