If you're using the full fuelly site, click on your vehicle's profile and scroll down. You should see a link on the right towards the bottom asking if you want to share your data. That will take you to a page to get the badge code which you then copy and paste into your signature (which is under "user cp" at the top of the forum page on fuelly)
I have the BBC sig code but can anyone tell me why when I use it in a forum on another site I don't see the nice image of my car but the default "econo logo"
Here (below) it displays as it should, there...not so much