Signature Heroes
From City of Heroes: Rebirth - Wiki
Overview
Signature Heroes refers to the NPC heroes of Paragon City. The phrase usually means the most famous of all heroes, especially those used in marketing of the game. Signature Heroes are found as trainers in many zones of the city, and are also the ones who give out many Task Forces in the game. In some cases, certain Signature Heroes will fight along side you in your missions.