<a href="https://en.wikipedia.org/wiki/National_Security_Agency" class="extiw" title="en:National Security Agency">National Security Agency</a> (NSA) security/motivational poster from the 1950s or 1960s.
<a href="https://en.wikipedia.org/wiki/National_Security_Agency" class="extiw" title="en:National Security Agency">NSA</a>
<a rel="nofollow" class="external free" href="http://www.governmentattic.org/28docs/NSAsecurityPosters_1950s-60s.pdf">http://www.governmentattic.org/28docs/NSAsecurityPosters_1950s-60s.pdf</a>