The Society Against Evil is an organization that fights against the evil spirits. The group was first mentioned in the episode, An Invitation.
During Season 1, the Society Against Evil marked clues with their symbol all over the Mansion, so that the guests could find their way out.
While they didn't appear through out the season, during the opening scene of The Sorceress, two Society members are seen taking the Crown of Oblivion and destroying it before being attacked by the Sorceress.
Joey was killed at the end of The Sorceress by the Sorceress, and he meets some Society members at the gate between the living and the dead. They offer him the chance to return to the land of the living. They have Joey sign a contract in blood, saying that he would sacrifice his friends at the chance to live again. Their symbols are seen through out Everlock. They were also the ones to originally to trap the Carnival Master.