The number 52 appears in every episode of the first season.
When Barry is showing S.T.A.R. Labs his power, the camera pans to a billboard for Ferris Air. Ferris Air is the employer of Hal Jordan, the alter ego of Green Lantern.
Mark Hamill has played all on-screen versions of The Trickster/James Jesse including the original "The Flash (1990)" TV series and "Liên Minh Công Lý: Không Giới Hạn (2004)," as well as this one. His costume from the original series was also shown in his latest incarnation during the episode "Tricksters".
As a nod to "Học Thuyết Vụ Nổ Lớn (2007)," Cisco is seen occasionally wearing a 'Bazinga', a 'That's my spot' or a 'Rock/Paper/Scissors/Lizard/Spock' t-shirt in homage to Flash-loving, t-shirt wearer character, Sheldon Cooper. This creates a plot hole (of sorts) as Sheldon Cooper wears flash t-shirts and talks about the tv show.