Baby Boomers might recall it through a swirl of tear gas, scrawled on walls, on signs in marches and silent sit-ins, or on the helmet covers of Vietnam soldiers.

Baby Boomers might recall it through a swirl of tear gas, scrawled on walls, on signs in marches and silent sit-ins, or on the helmet covers of Vietnam soldiers.

The peace sign, which turns 50 in April, was introduced in a calmer Britain in 1958 to promote nuclear disarmament, and spread fast as times got tense.

National Geographic Books is out with "Peace: The Biography of a Symbol," by Ken Kolsbun and Michael Sweeney, which traces the simple symbol from its scratched-out origins based on the semaphore flag positions for N and D (nuclear disarmament) to the influence it had, and retains, in social movements.

The symbol itself was created by a British pacifist textile designer, Gerald Holtom, who initially considered using a cross but got an icy reception from some of the churches he sought as allies.

While Holtom designed the symbol, the U.S Patent and Trademark Office ruled in 1970 that it is in the public domain.

It was quickly commercialized, showing up, among other places, on packages of Lucky Strike cigarettes, but also on a 1999 postage stamp after a public vote to pick 15 commemoratives to honor the 1960s.