Photobucket has thumbnails... its the things you see when browsing your album. Right click then click properties. Copy the image location. It should have "th_" before the image name.
Then put it in like this....
CODE
[URL=http://i126.photobucket.com/albums/p120/skSkareKrow/sksig.jpg][IMG]http://s126.photobucket.com/albums/p120/skSkareKrow/th_sksig.jpg[/IMG][/URL]
Putting the thumbnail image as the IMG and the normal size image for the URL.
Translated, it comes out as a clickable thumbnail.

Rifleman's way is just like mine, only less complicated. lol