Switching off digital signatures in Entourage

I somehow accidentally switched on the digital signature function for email through Entourage, and would like to turn it off. Can't find directions for doing so. I get a message saying that I must first install a valid signing certificate, and do I want to send an unsigned message. Big waste of time for me, don't have a signing certificate, not even sure how to get one or what utility this function actually is...

Thanks in advance...