Justice League may have finished its theatrical run as the lowest-grossing installment of the DC Extended Universe to date, but the film has provided a wealth of material for dissection, from deleted scenes and hidden references to concept art to, um, a peek at Steppenwolf's bare butt. However, closer inspection of the home release has unearthed a clever callback to the 1960s Batman series.

Spotted by Redditor officialjfftv, the nod to the beloved TV show comes early in the film, when Ezra Miller's Barry Allen pays a visit to his imprisoned father. After the fledgling superhero signs in at the prison, Bruce Wayne's informant, Officer Ben Sadowsky, surreptitiously places a call so the Dark Knight can track the young man back to his hideout. Although viewers may have been distracted by the fact that the prison guard is played by Marc McClure, best known as Jimmy Olsen from the Superman films, the real Easter egg is on his phone.

When the officer makes his call, the icon of red phone appears on his screen in a nod to the Batphone made famous on the Batman television series.

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Actually introduced (although not by that name) two years earlier in DC's Detective Comics, the Batphone became legendary on the TV show as the hotline between Commissioner Gordon and the Dynamic Duo. Of course, there were at least four red Batphones on Batman:in Commissioner Gordon's office, in Bruce Wayne's study in Wayne Manor, in the Batcave and, in slightly different version, in the Batmobile.

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Available now on digital HD, Blu-ray and DVD, Justice League stars Ben Affleck as Batman, Gal Gadot as Wonder Woman, Henry Cavill as Superman, Amy Adams as Lois Lane, Jason Momoa as Aquaman, Ezra Miller as The Flash, Ray Fisher as Cyborg, Jeremy Irons as Alfred Pennyworth, Diane Lane as Martha Kent, Ciarán Hinds as Steppenwolf, Jesse Eisenberg as Lex Luthor and J.K. Simmons as Commissioner Gordon.