I also think you are wrong to demand the signature be removed. It wasn't/isn't overboard, obtrusive or obscene. We all have the option of turning signatures off if they distract.
Even if this were a stock only site you have a poor argument since you offer the ability to add a signature (and a quote) to ones profile.
Your personal aversion to religion and/or politics (especially since there are boards for both) should not be a factor in your administration of the site. If that's your sole reason for putting lmorovan in jail... you're making an issue where there need not be one.
It would be easy enough to avoid, though... remove the option of having quotes and signatures.