Zack Snyder's Watchmen movie subtly confirms that Batman isn't a part of the film's DC universe. Alan Moore and Dave Gibbons' Watchmen story exists more or less within its own alternate continuity, within which many of DC's characters are actually fictional superheroes. The same is true of Zack Snyder's 2009 Watchmen movie which, until the ending at least, was a relatively faithful interpretation of the source material in terms of story and character. The Watchmen world is one in which pulp superheroes inspired a spate of vigilantism and the emergence of Dr. Manhattan allowed the United States to win the Vietnam war.
Nevertheless, Watchmen does exist within the DC Multiverse and the 2017 Doomsday Clock comic series married together the world of Watchmen with the wider DC Universe. Although there's some debate as to whether Doomsday Clock is a sequel to the original Watchmen or a separate story altogether, the miniseries introduces Dr. Manhattan and the gang to the likes of Superman and Batman in previously unseen ways. Doomsday Clock places Watchmen in its own section of the DC Multiverse, but still maintains that the two universes see each other's vigilantes as fictional characters.
While there's a degree of ambiguity to the relationship between Watchmen and the rest of the DC canon, Zack Snyder had a little Multiverse fun with his 2009 movie adaptation of Moore and Gibbons' graphic novel. Watchmen's opening credits takes the form of a montage recounting the history of the titular vigilante group. To the familiar sounds of Bob Dylan, viewers get a crash course in the background of the Watchmen and one particularly memorable scene shows Nite Owl fighting off an armed thug. The brief image might seem innocuous at first, but looking closer, it seems the man and wife Nite Owl is protecting are none other than Thomas and Martha Wayne.
The building the incident is occurring next to has a sign saying "Gotham Opera House," and the familiar necklace of pearls can be seen around the neck of the female victim, while Thomas Wayne grips his gloves tightly. Even stranger, advertising posters for the first issue of Batman can be seen on the adjacent wall. On the surface, this scene appears to be a double-barreled Batman Easter egg, simultaneously aping the origins of the Caped Crusader and establishing him as a fictional character.
Given that almost anything can happen in the Multiverse, however, there could be an even more fascinating interpretation of this shot. The comic books have demonstrated that the cast of Watchmen are fictional characters in the DC Universe and vice versa, but could that be because the vigilantes in the Watchmen reality replaced them? Does the Bruce Wayne of the Watchmen world avoid becoming Batman purely because Nite Owl stops the fateful Wayne murders from ever taking place? It's certainly an interesting thought, even though Snyder most likely just intended the scene as a cool nod to a DC favorite, but maybe the world of Watchmen would've been very different if Nite Owl hadn't taken a midnight stroll down a theater alleyway. Alternatively, is this scene not an actual mugging, but Hollis Mason recreating a famous scene from an in-universe comic book for the benefit of the cameras?