The most famous postwar logo without commercial purpose -- or, at least, intended commercial purpose -- the peace symbol, turns 50 tomorrow.

Adopted with stunning speed by dozens of counterculture movements in the 1960s, its message expanded and now most people see it as a generic symbol of peace, adaptable to almost any pacifist cause.

"The peace symbol continues to exert almost hypnotic appeal," writes Ken Kolsbun in Peace: The Biography of a Symbol, which will be released by National Geographic's publishing arm in April.

"It has become the rallying cry for almost any group working for social change."