Suicide Squad: 14 Obscure Easter Eggs You Probably Missed
3. The Stabbed Bat
David Ayer said that all of the Joker's tattoos would be Easter Eggs (though not all of them really are), and smartest is the stabbed Bat on his left bicep. That relates back to The Dark Knight Returns, which sees Batman and Joker in a final battle that eventually sees the Joker die, but not before he repeatedly stabs Batman in the stomach.
There's also a Death Of The Family Easter Egg on his back: the horrifically grinning jester wielding a hammer is very reminiscent of the look of Mr J in that iconic modern arc...