nicely worn and weathered vintage american industrial heavy cast iron railroad wayside "whistle" signal sign fabricated by or for the pennsylvania railroad. the weighted single-sided sign contains a keystone profile, with embossed edge and oversized letter "w" finish in black. the recessed region contains a largely intact white paint finish. the sign was originally posted on a six foot steel pipe. a whistle post is a sign marking a location where a locomotive engineer is required to sound the horn or whistle. whistle posts in the united states were traditionally placed about one-quarter mile in advance of a road crossing. the signs in themselves varied in design from railroad to railroad. generally, even if the advance warning provided by the horn will be less than 15 seconds in duration this signal is to be prolonged or repeated until the engine or train occupies the crossing; or, where multiple crossing are involved, until the last crossing is occupied. the same rule is practiced when approaching locations such as rail yards, where men may be working on the tracks as well as bridges, tunnels and other points. measures 16 x 16 inches.