When DC Rebirth kicked off, Batman found the blood-dripped badge of the Comedian embedded in the wall of the Batcave, leaving him very confused but confirming to us that the world of Watchmen was coming to the DC universe. Since then, nothing much has really happened with it—but starting this April, that will change.
Source: io9 – Batman and the Flash Are Teaming Up to Uncover DC Rebirth’s Watchmen Mystery