Actually, i think it probably DID take your edit, but was showing you the old copy in your temporary internet files. I often have to refresh to get edits to show up because my browser thinks it's got the most current image in it's local cache.
In the above sig example, clicking on the image will take you to a link.
Use this without the paranthesis:
(<a href="the link address"><img src="the image address"></a>)
And the image address can be gotten by submitting an image as an attachment and querying the address in the usual ways as described above in this thread by Weird Harold and others.