Not since Shyamalan surprised us with the reveal at the end of The Sixth Sense has one of his twists worked so well ... which is why it's doubly surprising that he sort of spoiled it himself. Displaying a Batman-villain-like knack for leaving clues, Shyamalan hinted at the twist in the movie's poster. The Split and Unbreakable posters feature a similar cracking glass motif:
Universal Pictures, Touchstone Pictures
Not only that, but when you place the two posters side by side, the cracks almost connect -- as if it's one pane of glass that's broken. This could very well be linked to the theory that Mr. Glass was responsible for activating Split's protagonist's powers. Whatever the case, it should now be way easier to tell which Shyamalan movies to skip. If the poster shows glass and/or Bruce Willis, go see it. If not, you're good reading the ending on Wikipedia.