In 1966, Bob Noorda, a Dutch-born designer, spent three weeks navigating New York’s subway system, pretending to be a commuter and trying to follow the signs from one train to another. What Noorda found was chaos: the walls bristled with arrows and impossible-to-follow instructions. The New York Transit Authority was hoping that Noorda and his firm, Unimark International, could fix the problem.

It was an era when graphic designers hoped to reinvent the world, and Marshall McLuhan declared, “We become what we behold.” The team at Unimark wore lab coats, and at one point they drafted a manifesto declaring their allegiance to sans-serif type. When Noorda and his partner Massimo Vignelli took on the subway signs, they didn’t just update them — they invented what they thought of as a new grammar for New York City. They used minimal text, arrows only when necessary and color-coded discs to indicate different train lines. The discs were Noorda’s masterstroke.

Subway riders could navigate from dot to dot, in much the same way that hikers traverse a forest by following trail blazes.

The signs also had to project an aura of officialdom. As a rider, “you want to know that all the signs are coming from a single voice,” according to Paul Shaw, a design historian and typographer. Noorda and Vignelli decided that New York’s “voice of authority” could be playful. Their signs popped with Crayola-like color and showcased a typeface called Standard that projected a Bauhaus cool.