There is little doubt that Birds of Prey (And The Fantabulous Emancipation of One Harley Quinn) is somehow set in its own little universe with no ties to previous DC Extended Universe movies. However, it looks like there's still an interesting little Easter Egg that connects the Margot Robbie film to The Suicide Squad.
SPOILERS AHEAD! YOU HAVE BEEN WARNED!
In Birds of Prey, a scene in the police station actually featured a surprise cameo from one of Harley Quinn's old friends. There is a photo of Digger Harkness aka Captain Boomerang mounted on the wall.
It's a surprising cameo considering that the cast and crew of Birds of Prey have already stated that there will be no connections to Suicide Squad. Although the picture of Captain Boomerang might be a harmless Easter Egg, some believe that it could mean something important in the upcoming DCEU flick. There is a possibility that Jai Courtney's character has broken out of jail and might be on the run by the time we get to see him again in The Suicide Squad.
For now, the premise of The Suicide Squad is still a great mystery. Hopefully, we'll get to learn more about the film really soon.
Birds of Prey also stars Ewan McGregor, Mary Elizabeth Winstead, Jurnee Smollett-Bell, Rosie Perez, Ella Jay Basco, Chris Messina, and Ali Wong. The movie is currently screening in theaters worldwide.