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.
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.
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 "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 (1999) 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 (2002) was exactly the same type of film as The Sixth Sense (1999).
The prints hanging over the fireplace and Graham's bed in the Hess's home are "Stone City" and "Spring Plowing," respectively, by American artist Grant Wood (1891-1942), who is perhaps best-known for his painting "American Gothic." He co-founded an art colony in Stone City, Iowa in the early 1930s.
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 (1987). 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.