Alrighty Smiley!
What you do is take the image url (That's under the sig picture)
Copy that, press settings on top near the top of the web page (Right to the "Send PM" Box).
Scroll down and look for a typing field call signature. Paste the URL in to that box, and then highlight the URL again.
Once Highlighted, click on the button with the tree on it directly below the sig box.
Save your settings and you'll be good to go! ^_^