Ok let me help you out there a bit step by step:
*Open/Edit one of your posts
*Use the Upload picture button, the one next to Upload Video, and select upload from URL.
*In a different tab open the page with the Signature picture, right click it and select view picture. Now copy this URL into the upload screen.
*It will generate a link for you you, use the first one with IMG sentene IMG
*Go to your signature and paste this link straight into the signature text square
*Dont use the "upload signature" or whatever option below that, it wont work
*After you just paste the Signature with the IMG in the text window, hit the save button
*Done. Marvel at your beautiful new Signature
Hope it helps. Seems like HungryHunter did something differently, because at one point he has the sig in some of his posts, but others dont have it anymore. Weird.