I asked that question, and here's the answer I got:
Here are the Ravelry buttons. Smaller is better. Save the button to your own computer and then upload it or embed into your signature through your USER SETTINGS. To link it just put the picture in and then click it so it's 'highlighted' then click the link icon and add the link.
http://www.ravelry.com/wiki/pages/Ravelry-inspiredworks