If you walked down Fifth Avenue in 1938, you would have seen a city full of people, traffic, and the tallest building in the world.

But the most striking sight was three stories up on a flagpole, a simple banner with five words on it: A MAN... WAS LYNCHED...

YESTERDAY.

How did that message end up flying over one of the busiest streets in America's biggest city?

And who was bold enough to put it up?

Lynching in the United States, by the 1930s, was an epidemic.

These barbaric public killings were used to terrorize Black citizens— especially in the south— into complying with Jim Crow segregation.

To put into perspective how bad the phenomenon was: according to a 1933 report by the Southern Commission on the Study of Lynching, between 1889 and 1929 almost 3,500 people were lynched.

That meant a man, woman, or child was hanged, or tortured, or burned alive every four days.

As a result of this terrorism, millions of African Americans fled to the North and West for safety, an exodus we now call the Great Migration.

But back to the flag in New York City.

Who unfurled that jarring message, designed to stop busy pedestrians in their tracks?

The flag was the brainchild of a fledgling organization called the National Association for the Advancement of Colored People, whose headquarters were in the building at 70 Fifth Avenue.

The NAACP was founded in the wake of a race massacre in Illinois in 1908, and it quickly moved to make ending lynching a primary goal.

For years, the organization lobbied state leaders and President Woodrow Wilson to pass anti-lynching laws, but nothing happened.

Then the NAACP gained a secret weapon.

His name was Walter White, an African American from Georgia, whose light skin and hair made it possible for him to pass.

In 1918, White, the NAACPs new assistant secretary, volunteered to go undercover in the south to investigate lynchings.

His reports were published in The Crisis, the NAACPs monthly magazine.

Shocking and graphic in their detail, the accounts were picked up by other publications across the country.

The NAACP had learned that its most powerful tool against white supremacist violence was publicity.

In just two years, The Crisis gained 50,000 new subscribers.

NAACP chapters multiplied across the country.

And then in 1920, the NAACP thought up yet another public message— the one on Fifth Avenue, on a six-by-ten-foot flag.

It was a provocative sentence, designed to be noticed even in a city where the fight for attention was nonstop.

The flag was just one element of a campaign that slowly, but surely, changed public opinion.

Lynching rates finally declined in the 1930s, largely because of the organization's relentless activism.

The flag was a bold enough element, though, that eventually, in 1938, the NAACP was forced to take it down or be evicted.

“We put the flag up outside the window of the office,” an NAACP executive later said of the idea, “alongside the American flags that flew so cheerfully up and down Fifth Avenue.

The owner of our building became so alarmed over the banner that he threatened to cancel our lease.

We had to stop flying it,” the executive remembered, “but we had made our point.” To learn more about how the NAACP fought back against racial violence watch FORGOTTEN HERO: WALTER WHITE AND THE NAACP from American Experience.