Wayside railroad signs were once a common sight along railroad tracks, and in the classic railroad era each company usually had its own style of wayside signs, although the whistle post became universal. The whistle post was a concrete post around 4 feet tall with a large "W" engraved or painted on it. It told railroad engineers to start sounding the whistle, usually two long, one short, and one long. Whistle posts were usually placed one-quarter mile in advance of a road crossing, rail yards with men working, bridges, tunnels, and other points, and the engineer would keep sounding the whistle until the train reached the crossing or other location.