In tomorrow's episode of Arrow, Oliver Queen name-drops Bruce Wayne and Gotham City.
Last week's season 6 premiere of Arrow saw Oliver outed on the news, with a photograph showing him in his Green Arrow costume but without a mask. In a press conference held at the top of next week's episode, Oliver suggests that it might be Photoshop, and that anybody could have been put in that costume, suggesting Wayne.
It is not likely that Oliver knows Bruce has his own...nighttime proclivities, given that there has never been any indication that he the pair know each other, or that Batman is a known entity in the CW's Arrowverse.
This is not the first reference to Bruce Wayne in the Arrowverse; in the series premiere of The Flash, a newspaper from the future indicates that Wayne's company and Queen's will merge in 2024.
Supergirl has directly referenced Gotham City before, as well -- and DC's Legends of Tomorrow has had Gotham come up in the random cycle of city names that appear in high-speed when the Waverider is about to arrive at its destination. Both Supergirl and Legends have made other allusions to Batman, but never used the actual name.
"I feel like we have our hands full with the crossover we're shooting right now," Supergirl EP Ali Adler said last season when pressed on Batman references. "I think people will be satisfied with how much crossover they're getting this season." Adler added, "We have this beautiful history with DC, and I like that we get to borrow from this amazing, wonderful canon that we have."
Arrow airs on Thursday nights at 9 p.m. ET/PT on The CW, following new episodes of Supernatural.