From Boing Boing 10 years ago: "Spammimic is a site that will encrypt short messages into email that looks like spam. The creators of the site designed it to be used in countries where it is illegal to use encryption."
Spammimic is still around! Since then, spammimic has come up with four other ways to encode messages: as spam with a password, as fake PGP, as fake Russian, and as hidden space and tab characters. All of these methods are probably pretty weak, but could be used to fool your parents or snoops at the company you work for.