Snyder added with the image: #SuperJedi.
If you take a closer look at the image, it appears as if Cavill is wearing the Superman costume underneath.
It's unknown what Snyder is actually trying to get across, other than having a little fun, but Snyder has been previously rumored for new Star Wars movies.
"Batman v Superman: Dawn of Justice" has a newly announced May 6, 2016 release starring Ben Affleck as Batman, Henry Cavill as Superman, Gal Gadot as Wonder Woman, Amy Adams as Lois Lane, Laurence Fishburne as Perry White, Diane Lane as Martha Kent, Jeremy Irons as Alfred, Jesse Eisenberg as Lex Luthor, Ray Fisher as Cyborg with Callan Mulvey, Holly Hunter and Tao Okamoto in new character roles for the film. Justice League is to follow directed by Zack Snyder as well.
For more news on the "Man of Steel" and related movies head on over to the Cosmic Book News Superman movie hub.