There used to be some restrictions on what you could do with the sig bit because sometimes the sigs can overwhelm the thread. But if it allows it then ill say how it ought to be done.
You need a URL block around the IMG block.
Code:
[ url = http://www.cartographersguild.com ] [ img ] https://www.cartographersguild.com/images/cartographer/misc/cartographer_logo_short.png [ /img ] [ /url ]
(No spaces in it tho)
Oh and if people link to really spammy stuff and it gets noticed and flagged via the widgets at the bottom of the posts then big heavy spam hammers come a tumblin' - Not saying that you will GreatWhiteNorth but this goes out to the more nefarious types we occasionally attract here at the guild who may be reading this...