Once I had a professor who had a top secret clearance and did some government work. He couldn't reference this because it's never been unclassified. But in one

Once I had a professor who had a top secret clearance and did some government work. He couldn't reference this because it's never been unclassified. But in one of his courses, he had an image of these two circles aligned just like this when discussing a relevant topic, and I don't know if anyone in my section picked up on it.