I have seen the t-shirt that says "You Don't Know Me" and has the Federal Witness Protection seal under it.
Apparently, the CIA did recruiting in the 60's or maybe 70's at ham fests (amateur radio swap shops). They signed up for a booth at the Atlanta Radio Club's hamfest and were given a table. They never showed up to the hamfest, but they will had a table with a sign above it. Someone took down the sign and wrote below their name "We are here, you just cannot see us."
-SquirrelNuts