Snakey copy the below info, go into the "Edit Signature", and paste it into the top section that looks like the section where you would type a post. After pasting it, remove the asterisks between the [img] and the URL address, and the ending [/img]. I had to add the asterisks otherwise, it just would have posted the image again. Then hit the "save" button at the bottom.

[IMG]*http://i36.tinypic.com/2hp0dxg.gif*[/IMG]