Matt,
I take it you know how to save the URL from the picture at your web site. Come back here, go into your profile and you'll see a block next to the word "signature". In that block put whatever words you want to show up in your signature and then put [ img]. Then put the URL next to the bracket and end the URL with a closing bracket like this [/img ]. There should be no spaces from the first braket to the last (I had to use spaces for it to show up here). The URL is taken from the picture itself and starts with "http" and ends with ".jpg"
Here's your PT.