Download the Firefox add-on below my signature
It puts a tiny rubber-stampy looking icon in lower right of your screen
Edit Signature
The insert-a-picture tool looks like a little yellow envelope next to the insert-a-link tool
Go to the photostream of "PM logo" on Flickr to get a weblink to the image
Right click on the thumbnail of the image called Mini PM (don't open the image) to get the link
Select "copy image location" from the dropdown to get the address called for
Click both Apply and OK
