Council Security are non-military personnel responsible for the security of the civilian institutions within the fleet. They guard the Quorum of Twelve and have jurisdiction over the prisoners of the Prison Barge. (Baltar's Escape)
During the run of the series, it was evident that Council Security was viewed with disdain by Colonial Warriors. (Greetings from Earth)
Due to the color of their uniforms, they are referred to as "blackshirts".