You don't sound stupid, it's an honest question. Ok, basically what you do is click on yourself, your own profile, and there you see your name and information. Below the mall part about Karma, there are a couple links to click, one of them is Edit My Signature, just click on that and your there.
Also, I'm not lecturing you or anything, but this section here is for people asking questions bout their Tamagotchi's, the actual toys and what not, so the next time that you have a question like this, don't put it here, put it in the sections farther down. There's one labeled (Non) Tama-Talk, maybe there.
Again, I'm not yelling at you or anything

welcome to the site and I hope to see you around