Imperial Security, also known as the Empire Security Service, was a branch within the Klingon Empire's government that was charged with ensuring that order was maintained on Klingon vessels. Its officers operated from a special selection within the pod of a starship. In this part of the ship, they keep watch over their comrades to ensure that order was maintained as well as ensuring that no activity that is not allowed takes place on a vessel of the Empire. (TOS video game: Starfleet Command Volume II: Empires at War)

They are also charged with watching over the subject races and ensure that they do not rebel against the Empire. (TOS video game: Starfleet Command)