I think the aliens came, saw and left!
The more time I spend around certain individuals from certain places, the more I believe in ancient aliens.
There is no way these people could have ever figured out how to stack blocks to make those pyramids in a certain Central American area.
Do the labor, yes. But put two and two together to design it, no.
The NSA has a severely redacted article on deciphering one of several ET messages from SETI on their public web site. Perhaps these fellows should start with that document.