Ah, I don't think so, maybe if you do a search you'll find one.
But, if you go to any image hosting site (
www.photobucket.com works fine for me), get an account (just follow the prompts and hey presto!), and upload your image, after you upload your image you scroll down to see the image, as well as 3 different codes: The
URL code, which is used for direct links, the
HTML code, and the
[IMG] code which are both used for posting images on forums, blogs etc.
The one you want is the
HTML code, which should be the second one down of you're using Photobucket. Copy and paste the HTML code into the signature (the big white one, not the little boxes) and you should have your signature!
If you have any further questions, feel free to ask on this thread or through PM. ^^ I don't pretend to be an expert, but I'll do what I can. <3