The skulls artistically convey the notion that the human mind itself is a crystal ball to the other side. I think of it as just having the power of art to project and to draw out inner human potential.
The legend of the appearance of all the lost skulls and their ability to stop the end of the world by some sort of magic circle may be just another way of bridging the gap between the material and the esoteric worlds and reaching the skeptics interested mainly in legitimate scientific energy by endowing the skulls with tremendous power of a substantial nature. Modern shamanistic writers may be behind the legend. One can call it a hoax but I can see the value in any hoax.
My question is if the storyline of the Russians looking for a skulls in Indiana Jones makes any sense historically? I seem to recall the KGB being interested in remote viewing of some sort but not much else. I can see why they chose to make the Communist villain a woman. Was she related to Rasputin, perhaps?