Random sig images?
All you need is access to a web host that supports PHP. Then, whip up a quick PHP script to randomly pick an image, and link to the script as though it was an image.
Example: You call your file r-sig.php. You put it into your signature like so:
[img]http://www.yourserver.com/r-sig.php[/img]

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Biggest Troll on the forums? I'll give you a hint:

Not sure if this is the right forum, but it seemed closest. Is there a way to have a different image appear in your signature every time a page is loaded? I've found a lot of scripts on the net to that effect, but they all rely on being inserted into the page itself, rather than calling on a script via embed.