|Population=UnknownNone

|Class=Unknown''Morti perpetua''{{Fn|3a}}|Tithe Grade=Unknown''Aptus non''

'''Signus Prime''' is was the main planet of the Signus Cluster, a tri-star system of seven [[Hive World]]s and fifteen moons. Once a major industrial center, the System of Signus fell prey to the agents of [[Chaos]] during the dark days of the [[Horus Heresy]]. It became a [[Realm of Chaos]], a system of [[Daemon World]]s, and fell under the rule of Kyriss the Perverse, [[Greater Daemon]] of [[Slaanesh]]. Kyriss raised for itself a vast palace on Signus Prime, the Cathedral of the Mark, and its [[daemon]]ic horde rampaged across the system, utterly destroying hundreds of years of civilization and annihilating several planets. The entire populace was either butchered, enslaved, or corrupted, and all hope fled its inhabitants. Deliverance was to comecame, ironically, in the form of [[Sanguinius]] and the [[Blood Angels|Blood Angels ]] Legion of [[Space Marines]], sent by the [[Horus|Warmaster ]] [[Horus]] to what was supposed to be their doom.{{Fn|1a}}

During the [[Horus Heresy]], Signus Prime was the site of an important battle between the Blood Angels and the daemonic armies of [[Ka'Bandha]]{{Fn|1}}After the battle, the entire cluster was declared ''morti perpetua'' ("forever dead") and quarantined. The Blood Angels expunged all records of their presence on Signus, resettled the few living survivors in neighbouring systems, and deployed beacons to warn starfarers away from the Signus system{{Fn|2a}}. They also deployed a tactical cyclonic device to destroy the Cathedral of the Mark and a massive chunk of the continent with it{{Fn|3a}}.