Not sure how crop circle pop up here, but it's possible that aliens would be making them. Not saying it's the most probable but possible. You're assuming aliens would be logical and have no interest in making them. When it's possible they can be irrational like humans who do things like spray painting walls and calling it art. Keep an open mind. Ghost I still don't believe. Add zombies to the mix. And vampires.
Spray painting walls is about marking territory, signalling outsiders who claims the area. Very primitive and old and entirely rational. Only later it was called art.