Signs is more than twenty-years-old now; so, you shouldn't bitch to me about spoilers.
It's probably a good film to watch over Halloween. It's still my favorite film by M. Night Shyamalan.
Just like most people, I saw it as an alien invasion movie for twenty years. It's still a pretty damn solid movie from that perspective; but, it creates logical problems. Not the least of which -- why would aliens that can't touch water invade a planet that's mostly water? Wouldn't it have rained somewhere?
So, through a few sources, I've heard a convincing counter argument to the idea that it's an alien invasion idea -- what if they're demons?
You never see a space ship in the film.
The creatures aren't little green men.
They have trouble getting through doors.
Mel Gibson's daughter in the film has an obsession with clean water. It's also said in the film that she was like an angel. It's also shown in the film that she might have some capacity to see the future.
It's cryptically noted in the film that, in the Middle East, forces had found a way to fight the creatures.
So, what if it's not water that kills them -- but holy water that kills them? What if the daughter actually is an angel?
Looking at the film from this perspective made it even better for me.
Clarification, there is a scene in which lights are seen in the sky. That throws a wrinkle in the demon theory.