The official teaser trailer for Season Seven of Game of Thrones — titled "Sigils" —  opens to ominous music. We hear a woman say the following: "I know what my father was, what he did." As she says this, and as other cryptic lines of dialogue are spoken, stone renderings of the house sigils for the duelling families are featured. We see a three-headed dragon, a stag, a wolf and a lion, presumably meant to represent Targaryen, Baratheon, Stark and Lannister, respectively.
As the trailer ends, the stone figures crack and crumble, falling into a formation that resembles the corpse patterns the White Walkers produce following a killing. Finally, a flash of green light appears and Jon Snow's voice is heard. He says, "There's only one war that matters: the great war, and it is here."