Your sign is from what was in it's time the UPS/FexEx of today they operated by rail all across America their railcars were what we call headend cars and were the hottest cars we would move they had the same set up as FedEx and UPS with pick up and drop off's at Depot's and General Store's as well as delivery by truck, wagon and air.
The signs go anywhere from 200 to 500 depending on condition I've seen a few on Ebay lately I picked mine up for 200 off of Craigslist and was from a D&RGW depot west of Denver, I brought it back to my Depot at Lasalle CO and put it in my office and I'm now looking for the red 3 foot diamond shaped sign to add to it.
A little more Info....
REA Express, Inc., formerly (1918–29) American Railway Express Company, or (1929–70) Railway Express Agency, Inc., American company that at one time operated the nation’s largest ground and air express services, transporting parcels, money, and goods, with pickup and delivery.
American Railway Express Company was established by the U.S. government in 1918, during World War I, at the same time that the government took over the nation’s railroads. The domestic express businesses and property of the nation’s major express carriers—Adams & Company (founded 1842), American Express Company (founded 1850), Wells, Fargo & Company (founded 1852), and Southern Express Company (founded 1861)—were expropriated and merged into a public corporation. After the war the domestic express businesses were not returned to their original owners (unlike the return of the railroads) but remained with the American Railway Express Company.
On Dec. 7, 1928, however, 86 of the nation’s railroads joined in setting up Railway Express Agency, Inc., which in 1929 bought out the American Railway Express Company and proceeded to operate the express business under private ownership. Forty years later, a group of the company’s officials secured controlling interest in the company, and in 1970 the company’s name was changed to REA Express, Inc. Faulty management, strikes by the Brotherhood of Railway & Airline Clerks, and competition from the U.S. Postal Service and United Parcel Service led to drastic financial losses, and on Feb. 18, 1975, REA filed for bankruptcy and was adjudicated bankrupt the following November.