STEP-1, CREATE YOUR ASSET - USING MAX DIMENSIONS 600X120 [WIDTHxHEIGHT]
STEP-2, UPLOAD IT SOMEWHERE CONSTANT AND USE A FIXED NAME IN OTHER WORDS A PLACE THAT WILL NOT REMOVE YOUR PIC, OR SUDDENLY DISAPPEAR [MGUPLOAD XD], AND NAME IT SOMETHING MEANINGFUL IE, FORUMPIC.JPG/.PNG/.GIF ETC...
STEP-3, GO TO YOUR PROFILE AND IN THE SIGNATURE SECTION [YOUR PROFILE IS AT THE TOP CLICK "PROFILE" AND IN THE EDIT BOX, THE BIG ONE... TYPE THE LINK ADDRESS FULLY QUALIFYING ADDRESS AS BELOW...
[center ][href=http://www.domain.com][img ]http://www.domain.com/asubfolderifany/forumpic.jpg[/ img][/ href][/ center]
[parts in UNDERLINE are optional if you want it centred like mine, parts in BOLD are optional too if you want a link to your blog or website etc... and the parts in italic the IMG bits are the minimum required to have just an image plain and simple...]
side note the profile signature box has a character limit too so be careful typing too much there... you also have the option of having plain [BLUE] text below or above your sig too just type them outside of your IMG /IMG or HREF /HREF tags
I hope this helps
EDIT
Update... I had to create spaces netween some sections like [href] [/ href] remove that space between the / and f to be /href with the brackets
EDIT
Another update... if you want it animated like mine... then use ANIMATED GIF format, bear in mind this reduces your colour palate to 256 colours... and limited transparency abilities