15 U.S.C. § 318 : US Code - Section 318: Weather signals on mail cars

Search 15 U.S.C. § 318 : US Code - Section 318: Weather signals on mail cars

The Secretary of Commerce, in cooperation with the United States
Postal Service, may arrange a plan by which there shall be
displayed on all cars and other conveyances used for transporting
United States mail suitable flags or other signals to indicate
weather forecasts, cold-wave warnings, frost warnings, and so
forth, to be furnished by the Secretary.