1.If you blink during Harley's introduction, you might miss the text that quickly pops up and reveals that she played a role in Robin's murder.
2.During Deadshot's introduction, he's seen in the same pose as he was in on the cover of the Secret Six#15 comic.
3.During the introduction to Dr. June Moone and Rick Flag, we see June in a bathtub filled with grass — specifically panicum capillare, aka "witchgrass." It's known to be used to stave off evil or attract lovers, both of which apply to June/Enchantress's story.
4.When Captain Boomerang is first introduced, the Australian super villain arrives in a bag that's labeled from Australia.
5.When the Joker is shown in his home surrounded by a bevy of weapons, there are also baby clothes, indicating that perhaps he and Harley want children. Later in the film, Harley even daydreams of a normal life with her, the Joker, and their little ones.
6.A shot of Amanda Waller's phone reveals that her service provider is Lex Luthor's company, LexCorp.
7.The text written all over the display behind Harley says "Si vis pacem para bellum." That translates to, "If you want peace, prepare for war."
8.There's a subtle nod to DC's The Watchmen when Deadshot stands in front of a giant smiley face display, which resembles The Comedian's badge, minus the blood splatter.
9.That guy shooting from the helicopter the Joker hijacked isn't a random dude; he's one of his henchmen in the comics, named Jonny Frost.
10.The gold gun the Joker fires from a helicopter looks a lot like the gold gun Michael Peña's character finds in End of Watch, which, like Suicide Squad, is a David Ayer movie.
11.Harley Quinn is briefly seen wearing her red and black outfit made famous in Batman: The Animated Series. She's dancing with the Joker, recreating the cover from the Batman: Harley Quinn comic.
12.The image of the squad being monitored on Amanda Waller's phone depicts a headless Slipknot after he's executed for trying to flee.
13.Deadshot's collar has the text "I AM THE LIGHT, THE WAY" on it, a reference to Bible verse John 14:6, which says: Jesus answered, “I am the way and the truth and the light. No one comes to the Father except through me."
14.The book Harley Quinn is seen reading in prison is fitting of she and the Joker's story. Here's how Amazon describes the story: "A bad boy rides into town on his motorcycle — and teaches the girl next door to lose control when it comes to desire."