Well first, you need to save the picture onto your computer, then upload it onto your own host or a public one, such as this one: 
http://imageshack.us since Arweb doesn't permit hotlinking.
Then you basically use this code:
Code:
[img]http://InsertImageLinkHere-NoSpaces.jpg[/img]
Replace the fake link with yours, and paste that whole thing into your sig!  Simple as that. 
