In 1967 the New York City Transit Authority hired Massimo Vignelli and Bob Noorda of the design firm Unimark International to design a signage and wayfinding system that would solve the problem underground.

The work they delivered, the 1970 New York City Transit Authority Graphic Standards Manual, succeeded in that goal and, perhaps unintentionally, the Standards Manual became one of the world’s classic examples of modern design.

-via the Kickstarter campaign to reprint the manual

More history on the book and the campaign over at the book’s project website.