This Colt Police Positive Revolver shipped to the Railway Express Agency, H.E. Wilson, Supt. in Chicago, IL on October 15th, 1930 in a 50 gun shipment. The factory letter notes that this revolver was factory rolled "Ry. Ex. Agy. on backstrap".
The REA or Railway Express agency was a national package delivery service that operated in the United States from 1918 to 1975. REA arranged transport and deliver via existing railroad infrastructure. It was created through the forced consolidation of existing services into a federal near-momopoly to ensure the rapid and safe movement of parcels, money and goods during WWI.