Set in the Objects.con and Weapons.con files for weapons and vehicles. This property links the object to the AI object made with AiTemplate.Create <name> in the corresponding AI/Objects.con or AI/Weapons.con file.
Every PCO (Player Controlled Object, e.g. a weapon or vehicle) needs its own section in Ai/Objects.con, so that AI (bots) can know about it. This is also required if you include another object (i.e. a turret mounted MG) which has its own code. Similarly, every Firearm you create in Weapons.con needs its own section in its Ai/Weapons.con.