If you want to make your sig a thumbnail like mine you need to go into photobucket and select the little box underneath it with the file name beside then go to the bottom of the page and click 'generate HTML and IMG code' once this page has loaded up third option is 'IMG clickable thumbnails for message boards - recommended' copy and paste this into your sig.
If a thumbnail is too small you can resize it in photobucket by using the edit options. I have resized this to the third option size (one size larger than thumbnail)