The option for animated signatures is in the Usergroups Manager, just pull up a usergroup and scroll down it will say:
Can Upload Images for Signature Yes No
Can Upload Animated GIF for Signature Yes No
Signature Image Maximum Width (pixels)
Signature Image Maximum Height (pixels)
Signature Image Maximum Filesize (bytes)
Mine are both set to YES for all usergroups on my site.
It is my "assumption" that is you have the first one set to yes that
vb is somehow converting all images to GIF format when storing them on the server hard drive in the file system. I have asked about this in the following topic on vbulletin.com:
Signature Pic - SigPic - use of JPG vs. GIF - vBulletin Community Forum
Can you tell me which table and which field you are reading the fileame value from for reviewpost? Is it table=sigpic value=filename or something else?