Joel Matheson recently attended the Warner Bros. Los Angeles Studio Tour, and fans who attend can pick up an official LA Studios Tours guide as a memento from the experience. The guide discusses the studio's past and current projects, including plenty of Justice League ads and materials.
Current Superman Henry Cavill appears in his regular Superman costume on one of the pages, but it is what's opposite him on the page that catches the eye. Next to him is a full shot of his costume, but this one is all black with silver highlights, including a silver S symbol on the chest.
That, of course, is a reference to the black suit Superman wears upon returning to the land of the living in the comics after he was killed fighting Doomsday. Underneath the suit is a caption referring to the many forms the character has taken over the years, but this is the current era's movie suit, so it isn't likely just a nod to comic fans.
That said, there's a chance it could also be the black Superman suit that Clark dons during Man of Steel during the skull dream sequence. If that's the case though, then they could very well reuse it in Justice League.
Many have suspected Superman would return in the black suit, as he is set to return in Justice League. Warner Bros. has kept him out of the promotion for the film aside from a poster or two, and even then he is in his traditional costume. There is a theory that he could emerge from his comatose state in a more berzerk or aggressive state, resulting in the League having to defeat him before he joins the team.
The black suit in the comics is simpler than this design, but going with this makes sense in the film universe. Zod had a similar black suit during Man of Steel, and if he does awake before he is truly ready, perhaps some of that militaristic viewpoint is the reason he wears this suit instead of his red and blue.
Who knows, but this latest glimpse does seem to indicate that fans will see the black suit in some form or fashion before Justice League ends.