Edit your signature using this link, if you don't know it already: http://forums.eyesonff.com/profile.php?do=editsignature

You'll want to mark it as an image. You can do this by either putting

[<i></i>IMG]http://www.site.com/image.gif[<i></i>/img]

or

<<i></i>img src="http://www.site.com/image.gif">

Either will work fine. I'm assuming you're able to upload the image to a website.