Right then, look top right and see a heading saying "Quick links", use the drop down list and select "Edit profile" then near the bottom look for the text box that says "Signature" and then upload your picture to photobucket.com and then copy the third text box under your pic (where it has IMG tags) into your signature text box in the edit profile bit and your pic will be displayed. Make sure you resize your pic though as big signature pics get on peoples nerves.
Oh yeah, turn off your caps lock too.