Is it a photo online, or on your desktop? If it's on your desk top, you're going to have to page @KnotPorscha to do that.
If it's online, you can do it yourself. First, find the photo you want online, then right-click on it and 'copy URL.' Then:
1. Go to 'Account Options' in the upper-right corner (looks like a little person head).
2. Go to 'Signature settings' on the left-hand side, under your photo.
3. Click in the signature code box.
4. Select the 'insert picture' icon (looks like a little Polaroid photo, right next to the 'insert hyperlink' tool, fourth active button from the right.)
5. Right-click and paste the URL you copied from the photo you want to insert. Hit 'submit.'
6. Hit 'save.' You're done!
I'm gonna go with 'not my circus, not my monkeys.'
Re: signature