The Klingon Imperial Guard was a civilian emergency-services organization. On Qo'noS and other major Klingon worlds, it carried out law enforcement, rescue and fire-fighting duties.
Members of the organization were addressed as Guardsmen. (KE novel: A Burning House)
Sorkav, son of Goryq was a member of the Imperial Guard, but was expelled due to a corruption scandal. (ST - Seven Deadly Sins novella: The Unhappy Ones)
In 2371, the Imperial Guard was infiltrated by men loyal to Chernoth. (DS9 comic: "Remembrance")