This film was shot in Newtown, PA. The scene which takes place in "2 Aldo's Pizzeria" is really a family-run pizzeria called "Mom's Bake at Home Pizza".
The film was shot on the property of an agricultural school, Delaware Valley College, where two areas of corn were already growing at different stages. The corn grown for the film was naturally further behind the other two areas of corn, so it was not a planned element.
The production used a new watering technique to make the corn grow faster which the Delaware Valley agricultural college was then very keen to adopt for themselves.
Rather unusually, James Newton Howard started scoring the film before it had been shot, as he was able to work from M. Night Shyamalan's detailed storyboards.
M. Night Shyamalan insisted that the film posters be released without showing Mel Gibson's face, as it is an ensemble piece, and that it didn't refer to The Sixth Sense, as it's an entirely different movie.
Only the scenes in the bookstore and the pizza shop were filmed in Newtown (Bucks County), Pennsylvania. The scenes of the house and cornfields were filmed on 40 acres that were leased to the film company by Delaware Valley College (an agriculture college) of Doylestown (Bucks County), Pennsylvania. After filming, the film company donated all the corn grown to the college's vegetable and fruit market. The house was built on the grounds and torn down after filming. Delaware Valley College is acknowledged in the credits at the end of the film. The drugstore scene was filmed in Morrisville (Bucks County), PA.
The scene in which Graham has his last conversation with his wife was scheduled for 12 September 2001, and was filmed after a cast and crew candlelight vigil.
In the part of the "Brazilian Video" the anchorwoman says the video was taped in Passo Fundo city that means "Deep Step", and what the boy's saying all the time is "It's behind that garage".
Just after the DVD is inserted into the player, and immediately after the Touchstone logo, a dark, fuzzy image appears in black and white, very quickly. It is a movie still with Merrill, Morgan and Bo sitting on the couch with the aluminum hats on their heads. The picture is shown even faster when "Play" is selected.
The Hess family hides in the basement, which Graham Hess says was once used for coal storage. In H.G. Wells's "The War of the Worlds", the main character hides from the aliens in a coal shed.
When Joaquin Phoenix is looking at a poster at the military enrolment office, he's looking at a movie poster of one of his own films (Buffalo Soldiers).
The "Brazilian Video" scene was actually shot in Miami, but the children were all Brazilians. A Portuguese couple was also brought to play their parents, but Shyamalan decided not use them because he noticed that their accent was totally different.
M. Night Shyamalan didn't want the trailers to make any reference to The Sixth Sense because he felt it didn't trust what was to come next. That it didn't give the film its own life, and audiences would assume Signs was exactly the same type of film as The Sixth Sense.
The trivia items below may give away important plot points.
The script originally called for the aliens to have a camouflaging ability much like the one portrayed by the alien in Predator. However, when M. Night Shyamalan's saw the ILM test shots of the creatures, he decided that it was too effects-heavy.
The aliens were originally scripted as having feminine builds and movements, thus the movements of tall, thin, female actors were used as models for CGI tests and some shots ("Brazilian Video"). However, it was decided that female bodies did not convey a threatening enough posture for the creatures, and a male CGI stand-in ended up being used in the final scene with Morgan as well as on the rooftop.