ABC kicks off promotions for Agents of S.H.I.E.L.D. season 2 with a mysterious new advertisement and a high-stakes online game.

In an impressively subtle bit of advertising, ABC has unveiled a new billboard promoting Agents of S.H.I.E.L.D. season 2. First spotted at a Los Angeles intersection, the new sign may walk the line between referential and “Huh?” for many who spot it.

But not in the case of Agents of S.H.I.E.L.D. fans.

Actor Brett Dalton (the devious former-agent Grant Ward) certainly understood the reference – and then added his own – when he posted an image of the sign on WhoSay.

The image, of course, refers to the bizarre mess of loops and lines carved by Agent Coulson (and earlier, John Garrett) in the eerie last moments of the season 1 finale.

Though the actors and showrunners have been zip-lipped on the strange subject, there can now be little doubt that the pattern will be a major story element in Agents of S.H.I.E.L.D. season 2.

Related: Showrunners tell the future – and the past – of Agents of S.H.I.E.L.D. season 2

In related news, Marvel has also introduced a viral website in promotion of the DVD and Blu-ray release of Captain America: The Winter Soldier. But this time, they went a little lighter on the ambiguity.

The website, ShieldvsHydra.com, invites fans to join the game as members of either S.H.I.E.L.D. or their persistent nemesis, HYDRA. After assignment, fans can participate in “missions” which earn entries into weekly sweepstakes – culminating in a chance to win a trip to the premiere of 2015’s Avengers: Age of Ultron.

The game definitely seems worth a look for Agents of S.H.I.E.L.D. fans. Though Agent Coulson and his team may have defeated the Clairvoyant last season, it’s clear that HYDRA will remain a force to be reckoned with in Agents of S.H.I.E.L.D. season 2. Reed Diamond will join the second season as serious HYDRA baddie Daniel Whitehall – and if we know anything about this show, it’s likely that that’s just the tip of the iceberg.

Agents of S.H.I.E.L.D. season 2 will premiere on September 23, 2014 at 9:00 p.m. on ABC.

Are you intrigued for the return of ‘Agents of S.H.I.E.L.D.’?