Get someone to host it on some webspace (I can do this, email it to me) and then in the forums here go up to the top left where it says "
user cp" and then go to the "
edit profile" section and find the box that's for your sig text. Put in: [IMG.]http://www.whatever.com/yoursigimage.jpg[/IMG.] (take out the periods in the IMG tags). Then save your changes.
Oh and just to let you know; If it's dirty or insulting it will be removed. So you might not want to have one described as you did above...