The movie suggests that something is written on the back of the Declaration of Independence. It is true that something is written on its back. The writing on the back of the Declaration of Independence reads: "Original Declaration of Independence dated 4th July 1776" and it appears on the bottom of the document, upside down. While no one knows for certain who wrote it, it is known that early in its life, the large parchment document (it measures 29 3/4 inches by 24 ½ inches) was rolled up for storage. So, it is likely that the notation was added simply as a label.
The water in the reflecting pool in front of the Abraham Lincoln Memorial, in the scene where Ben (Nicolas Cage) and Riley (Justin Bartha) are talking on the steps, was digitally added later, because the water was drained for maintenance at the time of filming. The pool was also digitally added in Forrest Gump (1994).
Ben, Patrick, and John Gates were all named after founding fathers (Benjamin Franklin, Patrick Henry, and John Adams). Abigail Chase is a combination of Abigail Adams, wife of John Adams, and Samuel Chase, a signer of the Declaration of Independence and later an Associate Justice of the United States Supreme Court.
When Gates is purchasing a replica Declaration of Independence in the gift shop, on the counter next to the register is a stack of books for sale. The book is "The Secret Architecture of our Nation's Capital" by David Ovason, and is about the Masons and the building of Washington, D.C. Ovason also wrote "Secret Symbols of the Dollar Bill", and U.S. currency is used as one of the clues in the film.
Before the movie got its rating, it was under the Touchstone Pictures banner (which is part of Disney). When the film got its rating (which is PG), it was then put under the Walt Disney Pictures banner, as it is clear that it is a more family-friendly movie.
In the Washington, D.C. segment, during the planning stage of the burglary, the movie cuts to an external shot of a building on the Potomac River, presumably where the bad guys are planning their attempt. This building is the Watergate Hotel.
Along with the Gates family all being named after founding fathers, Ian's (Sean Bean's) last name is Howe, the last name of two brothers who were a British General and an Admiral in the Revolutionary War.
While Gates is attempting to decipher the first clue on board the Charlotte, after Shaw suggests "Prison", Riley says, "Albuquerque. See, I can do it too. Snorkel". This is a reference to the 1998 "Weird Al" Yankovic song, "Albuquerque", which talks about a man's journey to Albuquerque with his lucky snorkel.
The Liberty Bell, shown in the movie, was made of styrofoam. The movie was shot a few days before the Liberty Bell was put in. This is proven by the fact that protective shades were installed in the observation window when the bell was installed. In the movie, Ian looks exactly where the shades are supposed to be, if the real bell was there.
On the yellow piece of paper, on which Ian (Sean Bean) was writing out the secret message contained on the pipe found on the "Charlotte", there was drawn, at the top of the page, two crossed swords with a circle between them. This drawing is the logo for Bean's hometown Football Club, Sheffield United, also known as "The Blades".
EASTER EGG: To see some hidden special features on the Region 2 DVD, navigate to the logbook in the upper right corner of the main menu and press select to enter, then enter the code "405" and select the "master code" for a list of all the special features available (some are otherwise only available in several hidden menus that must be found through mini-games on each menu).
The book that Ben shows Riley in the Library of Congress, that has the information about the Preservation Room, is called "The Earth System". It is some sort of a textbook, and it is authored by Lee Kump, James F. Kasting, and Robert G. Crane. The ISBN is 0131420593.
At the end of the movie, when Ben starts to tell Riley about the house he bought, the house actually belonged to Charles Carroll, the last surviving man who had signed the Declaration. This also happens to be the man who told Ben's ancestor the secret about the Charlotte in the beginning of the movie.
When Riley (Justin Bartha), at the end of the movie, says he got a measly one half percent of the treasure money. If Benjamin Franklin Gates' (Nicholas Cage's) earlier estimate back in the church with Sadusky (Harvey Keitel) of ten billion dollars is accurate, Riley would have made fifty million dollars.
When Ben is investigating the dead end treasure room near the end, and discovers the keyhole for the Charlotte pipe, a few bars of the underscore are from Pirates of the Caribbean: The Curse of the Black Pearl (2003). Both are Jerry Bruckheimer and Walt Disney projects.