oh..
Uhm ok do this:
1. Go to Settings (Upper right corner, in the same box as 'log out')
2. Edit Signature
3. Paste the Forum Image Code
I order to do that you need to save the image.
Then upload it with something like tinypic . com
After it's uploaded there should be a code that starts like this:
.......
That's the code you paste at Edit Signature