I don't hold with these new-fangled WYSIWYG editors so this is how to do it using the default html box. If you've changed the default in user cp to WYSIWYG you'll have to change it back to do this but you can put it back again once you've saved your sig.
1st, upload your sig pic
Copy the following code and paste it into your signature box [url="http://uk.ebid.net/stores/meebos-loft"][sigpic][/sigpic][/url]
preview (optional) DO NOT LEAVE USER CP UNTIL YOU HAVE SAVED IT!
Any problems send me a PM.