arrows

Mail in the 1920s was delivered by planes but they could only fly during the day.  Trains were used at night.  Several large arrows dot the country that were used as guides for the pilots.  There were also light beacons placed along the route that cut the coast to coast delivery time of mail from 83 hours to 33 hours.  I never knew that the arrows were there.  Now, I want to see one for myself.  route markings