Here’s another good one:

This-message-is-not-spam. If you file a spam complaint you will be deemed liable for all costs related to the spam complaint.

I’m not sure I’ve ever seen the words “This is not spam” in a message that wasn’t spam, or at least talking about spam. It’s kind of like “Please do not discard” on an envelope. It’s a sure sign of junk mail. I mean, if it was mail you wanted, you wouldn’t be discarding it anyway, would you?