When the aliens smashed to Earth, life changed. But not everybody figured that out right away. That's why the government had to blanket the country with PSAs like these.
These are original posters by awesome io9 art intern Daniel Spitzer.
You'd think people would know that messing around with aliens could screw you up in ways that make Hep C look like a paper cut. But it took years of reeducation before everybody got the idea, and you stopped seeing all those poor people with their venom sac infections waiting outside the free clinic.
Why do people always want to walk right up to a crashed space ship? Hopefully posters like these got the message through to looky-loos that these things are dangerous.
Sure, this seems obvious in retrospect.
As soon as the government realized that spider mummies couldn't cross water, everybody was told to dig moats around their houses. If only there had been PSAs directing them to clean up the mines before digging the moats, more lives would have been saved.