This Colt Detective Special shipped to the Colorado State Penitentiary in Canon City, Colorado on January 3rd, 1941 in a 4 gun shipment. The letter states this revolver was factory engraved with the following. "C.S.P. No. 2" on the butt of the revolver.
It was common practice where revolvers or pistols were used by multiple shifts that they would have rack numbers marking them so at the end of every shift a quick inventory could easily be taken.