From the start, The CW's "Arrow" has teased at its place in a larger DC Universe, dropping names of significance to fans of the source material into conversations, hinting at potential storyline directions. When it debuted in 2014, "The Flash" followed in "Arrow's" footsteps, namedropping characters and cities as it, too, built the idea that there's a while, big universe beyond the borders of Starling and Central City.

Over the weekend, "Arrow" Executive Producer Marc Guggenheim shared what he described as a piece of production art for the show's upcoming Season 4. The art, which appears to be a retro-style postcard, not only calls out the oft-referenced Coast City, but a more direct homage to the iconic oath of the city's legendary hero, Green Lantern.

Starring Stephen Amell, David Ramsey and Emily Bett Rickards, "Arrow" season four is scheduled to debut Wednesday, Oct. 7 at 8 pm EST on The CW.