"Arrow" season 4 continues to grow, as executive producer Marc Guggenheim just posted a link on Twitter that leads fans to a piece of production art alluding to the presence of another DC superhero: Green Lantern. There are no confirmations yet that a Green Lantern will make an appearance, but at least Coast City will. 

The photo appears to be a billboard for Coast City, which is where Hal Jordan — the most famous Green Lantern — comes from. The words "In brightest day, in blackest night, come to Coast City, when money's tight" are sprawled on the image, an obvious play on the Green Lantern oath. 

According to a report from Screen Rant, Coast City will primarily be used for season 4's flashback sequences, although the main characters may visit the location in a modern-day setting as well. It is also speculated that season 4's villain, Damien Darhk (Neal McDonough), and his organization H.I.V.E. will set their base of operations in Coast City. 

This will mark the first time fans of the series will get to see Coast City, but the location has been mentioned before. In the first season of "The Flash," Barry Allen (Grant Gustin) ran to Coast City in an instant using his powers to order pizza, and the city was also mentioned several times in previous seasons of "Arrow." 

As pointed out in the report, there are no confirmations of Green Lantern actually making an appearance on the show. DC Entertainment reportedly prevents their television shows from utilizing characters such as Green Lantern, Booster Gold and Harley Quinn because they have other plans for these characters on the big screen.

This does not entirely rule out a cameo appearance in season 4. There are other Green Lanterns other than Hal Jordan and John Stewart, such as Alan Scott, Guy Gardner, and Kyle Rayner. Any one of them might make a fleeting appearance in "Arrow" season 4 or even in "The Flash."

"Arrow" season 4 premieres this Oct. 7.