The group's insignia is two stars and a crescent moon superimposed on top of one another, along with the Greek letters NΨΞ. It can be seen on a map in the Observatory courtyard, on the metal grate at the entrance to its corresponding room, and on a decorative vane above that room.
The membership and exact goals of this society are still unclear. It is evident that Nu Psi Xi had something to do with the research of Mars, as the room marked by their insignia contains an interactive viewing screen which shows the interior of one of the Mars buildings. Whether they were aware of the Null or not while conducting their research remains to be seen.
The Craftsman was presumably associated with the group at one time, as they operated in Grey Holm and used technology manufactured by Talisman. By the events of The Room Three, however, no members besides The Craftsman apparently remain.