Last week, Arrow's creators made good on rumors that Batman villain Harley Quinn would make an appearance in the show (cameo here). Fool contributor Tim Beyers says there's reason for fans to believe we'll see more references to the Dark Knight's world before season 2 ends.

The next potential tie-in, Tim says, could come in episode 19. Titled "The Man Under the Hood," the story could refer to the original Red Hood from DC Comics lore, who goes on to become the Batman's arch-nemesis, The Joker.

Sounds crazy? Not if you look at the show's ratings and history. Season 2 hasn't drawn in as many fans as the inaugural, which averaged 3.68 million viewers per episode for The CW, a joint venture of CBS and DC parent Time Warner (TWX). Adding a major character like The Joker could build buzz ahead of the season finale, "City of Blood," which is due to air on April 30.

Meanwhile, intertwining plot points frequently refer back to Ra's al Ghul, an infamous Batman villain portrayed by Liam Neeson in Batman Begins and again in The Dark Knight Rises. Katrina Law plays his daughter, Nyssa, in the episode "Heir to the Demon," in which she's tasked with returning Sara (otherwise known as the heroine Black Canary) to the League of Assassins. Batman's influence is felt throughout Arrow, even if the Caped Crusader himself never makes an appearance.

Only the showrunners know how the story will play out. The point for both fans and investors is that, in referencing Batman's world so frequently, Arrow has introduced a model for creating a shared universe where callbacks, plot points, cameos, and the like stand in for expensive full-length guest appearances or movie-to-TV crossovers. The benefit? Fans get a taste of what the wider DC universe could become without promising too much, too soon, which Walt Disney (DIS -1.14%) may have done when it first unveiled plans for Marvel's Agents of S.H.I.E.L.D. last summer.

Instead of giving fans a platform for introducing new and emerging heroes -- what most of us had been hoping for -- the show has instead delivered a simmering spy narrative that's slowly building to a tie-in with next month's Captain America: The Winter Soldier. Warner and DC don't face those sorts of lofty expectations with Arrow. Yet that could change -- fast -- if the creators reveal tighter ties to the Batman universe before season 2 ends. Do you agree? Sound off in the comments section below.