Few days back, one of my friend asked me about how to edit the signature in forum profile. This is how it is done:
1. Login to your Forum Account.
2. Click on " USER CONTROL PANNEL" Tab.
3. Click on "Profile" tab.
4. Click on "Edit Signature" tab.
5. Now the main part. You need to use the "rokbox=" icon of the chat window just opened.
6. You need to paste a valid GIF url there.
7. Click on submit when you are done with the previous step.
And Bang! Your Signature is a animated one now. Congratulations.