Get yourself a gif (animated or otherwise) that you want, then use the img command (click on help on this page for the syntax) to display it in your sig box in your profile.
If you go to the Gen Discussion forum you will find many talented people who will happily help you with choosing and making a sig of your own, so I'll move this there.
Moved here.
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[This message has been edited by Memnoch (edited 06-09-2001).]