https://motherboard.vice.com/en_us/article/43548d/nsa-historical-propaganda-posters-foia

The National Security Agency isn’t just concerned with spying on the bad guys—and sometimes the good guys—or creating powerful hacking tools to pwn the world’s networks. The NSA has always been worried about employees spilling its own secrets, Edward Snowden-style.

In the 1950s and 1960s, the NSA made a bunch of posters to remind its employees that security is the most important thing, and that they must work hard to protect the country’s most important secrets. Thanks to a Freedom of Information Act request by the transparency site Government Attic, we can now see these quaint, sometimes hilarious, but also menacing, posters.