The conclusion of the episode teases the 4-part crossover between the show, The Flash (2014). Arrow (2012) and DC's Legends of Tomorrow (2016). The next installment of the crossover is The Flash episode 3x8 "Invasion!"
The Kryptonian symbology seen on the fortress display is the same symbology used in Smallville (2001).
This is Cisco's first appearance on Supergirl making him the second Arrowverse character to appear on all four of The CW's DC shows, ("Arrow" (2012) {The Man Under the Hood (#2.19)}), ("The Flash" (2014)), ("Legends of Tomorrow" (2016) {Fail-Safe (#1.5)}), & ("Supergirl" (2015) {Medusa (#2.8)})
The airdates of the Invasion crossover are: 11.28.19 Supergirl Medusa season 2 episode 8 11.29.19 Flash Invasion! session 3 episode 8 11.30.19 Arrow Invasion! season 5 episode 8 12.01.19 DC's Legends of Tomorrow Invasion! season 2 episode 7