In an interview with Entertainment Weekly, Guggenheim teased the idea even further, suggesting that a certain ring might maybe an appearance in the Season 4 premiere.
“There is a nod or two,” Guggenheim teases. “There is a billboard that people will get a kick out of, and there may or may not be a ring in the season premiere.”
That seems like a pretty clear reference to the Green Lantern’s power ring. If it does appear will it be on its own, or will somebody be wearing it?
It seems likely that the billboard will feature the Coast City travel image he tweeted out. Another possibility be an advertisement for Ferris Air. The Flash episode “Rogue Air” already mentioned that the company’s operations in Central City were shut down after “one of their test pilots went missing.” Hal Jordan maybe?