Before you think: “There’s another one who didn’t take his pills today”, please hear me out.
The idea that there is a chance that humans could one day could get into contact with extraterrestrial aliens (or that maybe this has already happened) is usually considered something that is only on the minds of Sci-Fi buffs or bona fide crazy people.
On the other hand, this issue is a subject which is discussed at least on a theoretical level by mainstream academia:
Both Voyager spacecrafts contained among other things a message by President Jimmy Carter:
The President certainly didn’t lend himself to a silly PR stunt, one has to assume that President Carter was advised that this was a reasonable thing to do.
Now here’s the question: Does the government, and by that I mean, any branch, the military, law enforcement, State Department, FEMA, Department of Justice, Department of Energy etc., consider the extremely remote possibility of a contact with extraterrestrial aliens serious enough to plan for such an event? Are there contingency plans for the day when a fleet of alien space ships shows up in the skies, Independence Day (the movie) style or, less dramatic, radio receivers all over the world suddenly start picking up a constant stream of messages?
One aspect probably is that the mere notion of the government considering aliens from outer space something to be reckoned with could easily be ridiculed and become fodder for all sorts of jokes. If there was no other reason to keep contingency plans secret, this would definitely be one.
(Please no conspiracy theories, stories of UFO abductions, Area 51 etc.)