When Arrow returns on Wednesday, October 7, the odds are good that his ever-growing team of heroes will get even bigger.

Today, executive producer Marc Guggenheim dropped a big hint about another A-list DC superhero who could be dropping by Arrow. Guggenheim tweeted what he called a piece of "production art" for the series' upcoming Season 4. You can view the image near the bottom of this article, but we'll save you the suspense.

It's a billboard ad for Coast City, the home of Hal Jordan, aka DC superhero Green Lantern. If that weren't a big enough clue for you, it also bears the tagline:

In brightest day
In blackest night
Come to Coast City
When money's tight

That's a riff on Green Lantern's famous oath, which is about twice as long but starts with the same two first lines.

So, what does it mean? Is this merely an anecdotal prop that we would never see up-close otherwise? Or is Mr. Guggenheim trying to tell us something? The latter is entirely likely, even if it there's no Lantern in the show's future. Producers of Arrow have already confirmed that some of the show's characters will visit Coast City for a multi-episode stay, so at the very least, viewers will get to see what this version of Hal Jordan's hometown is like.

However, what if Arrow really did want to introduce us to Green Lantern? Is it too much of a stretch to imagine that happening? It boils down to this: DC's television and big-screen units are separate entities, and while they (mostly) share their own respective universes, they don't cross over. At all. Ever.

Case in point: Superman is forbidden from showing up on CBS' Supergirl because he already stars in a big-screen franchise. For the same reason, Batman can't put in an appearance on Arrow or The Flash, even though he'd fit in nicely with that world. Smallville was famously never allowed to use Batman or Wonder Woman, because DC's movie department had plans for both of those characters at the time. The argument is that it would be confusing to audiences to have more than one incarnation of a character existing at the same time.

So, with Green Lantern already announced as a member of the Justice League (an actor has yet to be cast), you'd think that Hal Jordan would be off limits to the TV folks. All things being equal, he would be.

However, Warner Bros. muddied the waters last year when it announced that Ezra Miller had been cast as Justice League's Flash and would be getting his own solo movie in 2018 — after CW's The Flash had just debuted. Two Flashes, both by the name of Barry Allen, will (assuming The Flash is still on the air) exist simultaneously.

Does that mean the movie studio has loosened its standards a bit? Is there room in there for Green Lantern to squeeze through into DC's TV world? We'll find out this fall.

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