Signs is an Earth based science fiction which was released in 2002 and is directed by M. Night Shyamalan.
Aliens make signs in large crop fields as a precursor to attacking, presumably to signal one another. Once they lands, they venture out from their crafts only to discover they are dangerously allergic to water which covers 70% of the world. As a result, they leave the planet and its inhabitants alone. The story follows Graham Hess, a widowed priest who has turned his back on religion to become a farmer. His wife died in a car accident driven by a character played by the director of the film. He follows the events of the alien attack, their crop circles, attack and retreat.