For centuries, uniforms have been used as a way of identifying membership in a particular group.  This picture shows the winter Passenger Uniform of Mr. John H. Keller, train service employee for the Nickel Plate Railroad and Norfolk and Western Railroad, 1941 to 1974.  On most railroad lines, conductors, brakemen, station agents, porters and cooks wore uniforms.  Can you think of other careers that require uniforms?