Birds Of Prey: 10 References And Easter Eggs You May Have Missed

For comic readers, the name 'Janus Corporation' may have immediately raised some eyebrows, when seen written on the gate that Harley breaks through in order to destroy the ace chemical plant.

Because the Janus Corporation - as is very briefly alluded to in the film - is the company that Roman's family, the Sionis', owned before they died. While this company is known as Janus Cosmetics in the comics, it's probably a smart move that the company was moved away from makeup, as in the comics this leads to Black Mask's face being mutilated - whereas his film form is entirely unmarred.

However, the very important thing about this is that fans of Batman will have seen this reference once before, as we get a brief glimpse of the company's glowing neon sign in the Justice League film, suggesting these two universes can still be considered linked, albeit vaguely.