around WW2 and the early 50s, the octals pretty much all had stop signs. when 12A_7 took over, westinghouse, raytheon and RCA keep a horizontally- elongated stop sign. oh--tung sol, of course. they did also. i think a japanese manufacturer picked up that look, too. ge and CBS went to stencils and dots...i think westinghouse did dots as well, but i havent noticed.