This 1935 U.S. Mail Car is a hand painted, original prototype. Marx artists were no slackers! The details painted on this car are just incredible. Most people can't apply dry transfer lettering as well as this is painted.
Interestingly, the red 1935 baggage car never had these doors. As far as I know this design was only used on the green baggage cars.

Just look at the detail that was painted on this car! I'm afraid that digital art is replacing this talent. It's a shame.

(Courtesy of Fred Pauling)