How do I add a forum signature?

The forum I am currently using just has a text box for signatures so I don't know how to put one in. I want to use this a href="http://www.gifsoup.com/view/1751318/korn-falling-away-from-me.html" rel="nofollow"http://www.gifsoup.com/view/1751318/korn…/a as a signature but as you can tell I don't know how. Any help would be much appreciated