Null Signature System
First appearing on the SLDF's EXT-4D Exterminator and the later Spector, while the Chameleon Light Polarization Shield masked their visual presence, the Null Signature System cloaked their heat output and electronic emissions. While the system is engaged, the 'Mech is more difficult to track at anything other than short range, with the Beagle Active Probe and its unbranded Clan equivalent unable to locate a hidden unit with its null signature system engaged. Only the modern and experimental Bloodhound Active Probe can penetrate the null signature masking.
Like many pieces of advanced technology, the Null Signature System and the 'Mechs that carried it became LosTech during the malestrom of the early Succession Wars. Outside of the Word of Blake, all modern examples of the Null Signature System in the Inner Sphere are either experimental prototypes such as that carried by the Werewolf or exceedingly rare surviving examples from the original Star League, with the Capellan Confederation the Successor State closest to recreating the system. While not yet able to produce a bolt for bolt, circuit for circuit replication, with typical Capellan ingenuity House Liao has developed a stop-gap solution suitable for mass-production, the so-called Stealth Armor. Integrating the heat baffles and required components directly into specially designed armor plating, when linked with a Guardian ECM Suite Stealth Armor replicates its benefits (and disadvantages).
While the Clans retained the peak of the Terran Hegemony's military technology, the tenets of Clan honor find such stealth systems dishonorable and ceased research and production of the Null Signature System.
 Game Rules
The null signature system features heat baffles that mask the 'Mech's heat sinks and reduce its infrared signature. However, the baffles restrict the normal venting of heat, meaning the 'Mech generates an additional 10 points of heat while the system is active. The null signature system also incorporates a phased-array sensor system and a sheathed directional communication beacon. Therefore, a 'Mech with this system may not mount any special Targeting and Tracking Systems (including Targeting Computers, C3 equipment, and C3i equipment) or a Satellite Uplink system.
The null signature system does not weigh a significant amount, but does take up one critical slot in each of the BattleMech's hit locations except for the head, for a total of seven critical slots. A critical hit to any of these slots will disable the entire system.
- Maximum Tech, p. 91
- Tactical Operations, p. 336