The (Mostly) True Story of Helvetica and the New York City Subway details the use of type in signage, maps, and manuals for the NYC subway. A must-read for type and subway fans.
As if this plethora of signs were not enough, the subway system also had a bewildering variety of other porcelain enamel and hand-painted signs. The porcelain enamel signs, either hung from the ceiling or posted on the walls, were directional as well as informational. The directional signs included those on the outside of the station entrances as well as those intended for the corridors and platforms underground. Many of the informational signs warned against criminal, dangerous or unhealthy behavior: no peddling wares, no leaning over the tracks, no crossing the tracks, no smoking, no spitting. The directional and informational ones were made by Nelke Veribrite Signs and the Baltimore Enamel Company, while the behavioral ones were the product of the Manhattan Dial Company. Most were lettered in some form of sans serif capitals-regular, condensed, square-countered, chamfered, outlined-though some were in bracketed or slab serif roman capitals. They were usually white letters on a colored background (often dark green for the IND and dark blue for the IRT and BMT), yet many were also black on a white background. There was no house style.
What is to modern eyes a beautiful disorder of tiled text and hand-painted enamel became an embarrassing shambles in the 70s and 80s. It was only in late 1989 that Helvetica became the official typeface for New York City subway system signage…about 20 years too late to prevent the current signage from looking dated.