Snyder posted a photo to VERO that shows the image of Darkseid in a piece of ancient artwork. Based on a previous frame release by Snyder, it seems that this piece of art is being investigated by Wonder Woman.
Snyder released the image with the caption "A bell can't be unrung," quoting Lex Luthor from the end of Batman v Superman: Dawn of Justice, possibly confirming that Luthor was foreshadowing Darkseid's invasion.
Take a look below:
I can’t take these teases anymore!! pic.twitter.com/yaaigbJwFD— -/George\- (@kryptonscodex) November 25, 2018
It seems that Wonder Woman was investigating the history of the Mother Boxes. The artwork features Greek lettering, and so is likely ancient Greek art inspired by Steppenwolf's attempted invasion of Earth, which was repelled by the combined might of the Amazons, the Atlanteans, the Greek deities, and a Green Lantern.
Fans will notice what looks to be a mother box in the center of the image. The message here seems to be a warning, that the mysterious artifact has the power to bring forth the tyrant of Apokolips.
This image and the one Snyder released for Gal Gadot's birthday are just hinting at how much of Snyder's original plans for Justice League ended up on the editing room floor by the time the film was released.
Snyder left Justice League and was replaced with Avengers director Joss Whedon for reshoots. Snyder has continued to look back on the project though, releasing storyboard artwork and even trolling Warner Bros. on Thanksgiving.
Fans have rallied in support of Snyder with the "Release the Snyder Cut" campaign, an effort to see Snyder's version of the movie finished and released in a similar fashion to the Batman v Superman: Dawn of Justice Ultimate Edition. Snyder recently offered his thanks for the extreme measures some of those fans have gone to in their efforts.
Justice League is now available on home media.
Upcoming DC Extended Universe movies include Aquaman on December 21st, Shazam on April 5, 2019, Birds of Prey (and the Fantabulous Emancipation of one Harley Quinn) on February 7, 2020, and Wonder Woman 1984 on June 5, 2020.