Batman: Arkham Origins is the third entry in the highly successful Arkham series, and it is a prequel to the events of the first game. Because of this, there are many different secrets and easter eggs referencing both future events of the series, as well as the villains that Batman will fight later.
Some of the biggest easter eggs in the game can be found in the G.C.P.D Building. Among the site's secrets, there is a newspaper that celebrates the election of Harvey Dent to Gotham D.A. Dent, as many fans know, eventually becomes the villain Two Face and is a boss in the series. Another secret in the game that references Arkham Asylum is the locker of G.C.P.D officer Aaron Cash. Cash is the guard who gets his hand bitten off by Killer Croc during the first game in the series. Several chalkboards in the building also have listings for famous mob families of Gotham, such as the Maroni and Falcone families.
Two posters you can find while exploring Gotham City also give some nods to the origins of other iconic Batman characters. This includes Batman's sidekick, Robin, whose origin as a member of The Flying Graysons is seen in an advertisement. Another advertisement is for a movie starring Basil Karlo, who would eventually become the villain Clayface, and who has a memorable appearance in Arkham City. A final poster advertises an appearance from the magician Zatanna, who is a recurring DC Comics hero.
Blackgate Prison is also a good location for users to find secrets and easter eggs within Arkham Origins. One of the earliest easter eggs in the game is found in the visitor area of the prison, where players can see the name Jonathan Crane, aka The Scarecrow, in the visitor log. On the final mission players can find an air vent that, if crawled all the way through, will drop players into the cell of The Calendar Man. Finally, one easter egg involves The Joker singing "Jingle Bells, Batman Smells" parody song first popularized by "The Simpsons" and Batman: The Animated Series.
Finally, players can go to the place where Batman's parents were killed when he was a child, which is a traditional easter egg found in the series. The alleyway has the silhouettes of the two victims still on the ground, which players can find in an alley in the Park Row area.