Think Night of the Living Dead, only less creepy.
Like Unbreakable and The Sixth Sense, Signs takes place in Pennsylvania (my home state, incidentally), and in what seems to be the film�s most explicit homage to someone besides Hitchcock, the movie adopts, in its second half, the setup of George Romero�s classic horror film Night of the Living Dead, which was set outside Pittsburgh.
Even at the end of the film, after a blatant "Night of the Living Dead" rip-off, when he must deliver the goods, Mr. Shyamalan wisely opts for implication and reflection instead of gratuitous effects.
By leaving most of the menace to the imagination--and by borrowing from classics like "Night of the Living Dead" and "War of the Worlds"--he ratchets up the tension to nearly unbearable levels.
Shyamalan cites Invasion of the Body Snatchers, The Birds, and Night of the Living Dead as his inspirations for the way he wanted Signs to feel.
Before you can say "duck and cover," Shyamalan is rolling in the paranoia of "The War of the Worlds," "Close Encounters of the Third Kind," "The Birds," "Night of the Living Dead" and the full spectrum of 1950s sci-fi cinema.