Well, the first thing is to log in and go to Profile > Forum Profile Information. Scroll down, and you will see "Signature", with a white text box to the right of it. In order to write a signature, all you have to do is write something in that box.
If you want to put a picture in your signature, write this code there:
[img]IMAGE LINK HERE[/img]
In order to upload your own picture to use in your siggy, you must upload it to a a site such as tinypic.com. Once you've uploaded it, the site will give you multiple links, one of which will say "IMG Code for forums and message boards". Just copy and paste that link into your text box, and your picture should show up.
