Let's see if we can figure out where you are going wrong......
Ok, do you have the GB Badge in question already made? If so, upload it to your hosting site (i use Onfinite, but many use photobucket here. Both are free).
Once it's uploaded, go to the block where it gives you the web link (it should start with an http) and copy that.
Then come back to the forum here and go into update your profile. In the signature block portion, you will post it just like you would a normal picture on a thread. Only difference is that you have to manually type in the [img]'s, with you pasting the GB Badge link on the page.
Before you save your changes, it should look something like this:
[img*]pasteyourlinkhere[/img*]
just like that, except DON'T type in the *
once you save your changes, check any post you left before. If you see nothing right away, give it about 10 minutes, since it takes a little while for the forum to update itself. Give it a shot, and if you are still having trouble, lemme know. Good luck!