"This message may have been intercepted and read by government agencies including the FBI, CIA, NSA without notice or warrant or knowledge of sender or recipient."
...is a sig quote I first encountered in an email from my spouse.
He got it from a friend at the National Lawyers Guild (NYC). I found one instance of it online at Above the Law, from a NY Supreme Court Judge. (btw Can you spot the typo/misspelling on the website? In addition to fixing that, I'd also probably add a Boolean operator between CIA and NSA. /know-it-all-librarian-snark)
Having a signature quote like that is a nice in your face reminder that we're being watched. I think librarians concerned about privacy and government spying should consider using it, too.