In 1970 the New York City Transit Authority released this brand identity manual designed by Massimo Vignelli and Bob Noorda of Unimark International. Pentagram recently tweeted that it was found in a locker under some old gym clothes, and that their employees Niko Skourtis, Jesse Reed, and Hamish Smyth have created an online archive: thestandardsmanual.com where the book can be seen in its entirety.
Further Reading
The (mostly) true story of Helvetica and the New York City Subway