system
Given the following post, respond as if you're commenting on Reddit:
human
[Fallout] Why did Pre-War America know what the Zetans look like?

Not only is there a Zetan on the cover of an issue of Astoundingly Awesome Tales, there are also animatronic aliens in Nuka World. It seems that the US government was aware of their existance, along witht the Cabots and Hubologists, but the general population was not, as the aliens worked from the shadows, yet the Zetans can be seen in pre-war pop culture. The minigame Zeta invaders even mentions the aliens by name. While I know wild wasteland is not canon, even without Mothership Zeta the aliens make a lot of appearances in the series.
gpt
In our world, the popular idea of "little green men" came about around 1955, when ufo sightings and alien abductee stories became all the rage alongside the rise of science fiction films. However, the idea of "aliens" (both extraterrestrial AND mundane foreign) being green and small-ish has been around for centuries. 

We also know that the Zetans have been monitoring Earth for several centuries. So perhaps the pre-war American government knew all along what they looked like (as said in this thread, the Roswell incident was most likely a Zetan crash), and rumors/whispers/leaks of their appearance slowly made their way into prewar pop culture. Maybe someone in America was trying to send a message to the people, or perhaps the bastardized Zetan rumors just translated into the perfect pop culture villain to be fought and destroyed in various forms of media. It would have been a great distraction/change of pace from constantly seeing Chinese communists as the antagonists in everything.