For years, the signs in the New York City subway system were a bewildering hodge-podge of lettering styles, sizes, shapes, materials, colors, and messages. The original mosaics (dating from as early as 1904), displaying a variety of serif and sans serif letters and decorative elements, were supplemented by signs in terracotta and cut stone. Over the years, enamel signs identifying stations and warning riders not to spit, smoke, or cross the tracks were added to the mix. Efforts to untangle this visual mess began in the mid-1960s, when the city transit authority hired the design firm...