Last night's episode of Supergirl happened to feature a cool DC Easter Egg as a Legion Flight Ring was featured.
Now where did we see that before?
Nope. We see the rings and images are exactly the same from both episodes (see below).
The Flash is scheduled to crossover on Supergirl on Monday, March 28th with the episode titled "Worlds Finest."
"Supergirl" airs Mondays on CBS at 8pm ET; "The Flash" airs Tuesdays at 8pm ET on the CW.