Huge Elongated skulls, aliens. Out of place artifacts, aliens. TPTB, aliens. Ritual mutilation/sacrifice, aliens. Mysterious human origin, aliens. Complex ancient structures, aliens. Religious/spiritual entities, aliens. Atmospheric phenomena, aliens
the list goes on, feel free to add.
I have a theory that the government actually goes online and tries to shut down esoteric topics (spiritualism, herbal medicine, cryptozoology, and the like) through planting either extremely crazy sounding things, or by pure mockery. By focusing mainly on materialism, modern man has become docile and despondent and thus easier to control.