All he posted was an image of The Penguin from the comics, with no caption and no follow-up. Presumably, that's hinting he's signed on to play The Penguin.

It could be a red herring, certainly, but Gad's social media presence is a very carefully crafted one, as seen in his viral interrogation of fellow Murder on the Orient Express co-star Daisy Ridley.

There must be some very clear intent behind the tweet, with the timing of it making it a good fit for The Batman. That said, it could always be in connection with another DCEU project (Gotham City Sirens? Joss Whedon's Batgirl?), or even something else entirely, like an animated film.