Mysterious Agents Of S.H.I.E.L.D. Billboards Going Up In L.A.

Some mysterious new advertisements for the second season of Agents of S.H.I.E.L.D. have begun popping up around Los Angeles (via Entertainment Weekly).

They're particularly mysterious to anyone who didn't catch the show's first season finale. Those who did will recognize it as the strange alien equation that Agent Coulson etched onto a wall in the season's closing moments.

The advertisements have a minimalist quality to them similar to that of the early Season 1 advertisements, which simply featured the S.H.I.E.L.D. emblem. Of course, the S.H.I.E.L.D. emblem would be recognizable to anyone paying attention to Marvel Studios' films. The alien equation, on the other hand, will mean nothing to anyone who didn't watch Agents of S.H.I.E.L.D. last season.

Agents of S.H.I.E.L.D. returns September 23 on ABC.