Trivia: There is a theme of upside down being bad. The girl in the train stands on her head before the crash. The son is watching TV upside down. When Mr Glass falls down he falls on his back and sees the figure he is chasing upside down. When Bruce Willis breaks into the train wreck, the warning sign in the gates are upside down. Willis falls head first into the pool. The comic book given to Elijah is first viewed... you guessed it upside down! Not a mistake, but great directing.
Trivia: The first and last name of Bruce Willis' character, David Dunn, begins with the same sound, like other comic book heroes such as Peter Parker, Clark Kent, Matt Murdock, and Bruce Banner.
Trivia: Samuel L. Jackson's character, nicknamed Mr. Glass, is first seen as a reflection for each of the three ages he is shown as (We see him in a mirror after he is born, on a TV screen when he is 10, and on a picture frame when he is an adult.)
Trivia: The man that David Dunn stops at the football game is M Night Shyamalan the director.
Trivia: Samuel L Jackson has large hair to give a hint at the ending. Remember he says "Villains tend to have heads that are in disproportion to their bodies."
Trivia: The end credits list Robin Wright Penn's full maiden name as "Audrey Inverso". In keeping with the theme of the movie, the name sounds like a comic book character's name. The name Inverso also is consistent with all the reflective and upside down shots in the movie. Finally, the name is reminiscent of the "two sides of the spectrum" that Bruce Willis and Samuel L. Jackson inhabit.
Trivia: The logo of the TV channel reporting the train wreck is the same as the logo used by the Marvel superhero group The Fantastic Four. The logo can be seen during the news report about the accident.
Answer: Everything related to Samuel L. Jackson's character is upside down - to give a hint about his role in the movie.