Part of the massive world-building in Batman v Superman: Dawn of Justice was a shot of an encased Robin suit in the Batcave. Covered in graffiti and featuring a broken staff, it's heavily implied that the Joker killed this Robin.
In the comics, "Batman: A Death in the Family" is a story arc from Jim Starlin and Jim Aparo which featured the Joker killing the second Robin, Jason Todd. It's unclear if the first Robin, Dick Grayson exists in the DCEU but WB may have given indication that the suit in Affleck's Batcave belongs to Todd.
The below image was posted to the official Batman v Superman instagram account on April 27. In Death in the Family, the Joker killed Jason Todd on April 27. Is this an extreme coincidence or a meta-message from WB to its longtime comic book fans?