Go to ur profile and click edit my profile.

There will be a box named signature , you can put the html codes for the animated clips there and then click submit , now whenever you ans those clips will be shown with ur ans.

You can get those clips at many sites , e.g.  www.avatarsdb.com

Try this code

<a href="http://www.avatarsdb.com/"><img src="http://www.avatarsdb.com/avatars/neo_green.gif" /></a>