Click on your vehicle to bring it up. Scroll down, and on the right under the Tips you should see something about sharing your MPG. There is a label about seeing all the badges and stuff you can share. Click on that and follow its directions. Basically, you select your badge, copy the address into your clipboard, then paste it into the signature block (or wherever) where you want it to appear. It doesn't work on all sites, however, probably due to site limits.