I replied nicely the first time with a title of 'UNSUBSCRIBE', the full original message (including the header showing which e-mail address the message was sent to), and quotes from the CAN-SPAM Act of 2003 which says that there must be a clear unsubscribe mechanism (which there was not), and that requests must be honored within 10 days. This past week, I received more promotional materials and replied with an attached image of goatse.
I was contacted today by an officer in reference to "Unlawful Use Of Computerized Communication Systems". I was told that this could be prosecuted under state criminal law but that "since I had cooperated and returned the officer's phone call", I will instead be issued a municipal citation (locally adopted state law, references the same exact legal code 947.0125) for $300.
I fully plan on going to my court date to contest the citation on principle, but I thought maybe some other slashdotters might have had similar experiences or may be able to provide me with some basis on which to fight this."