Search: peace sign history
Why: Today I saw some douche with a decal of a peace sign upside-down on his back windshield.
Answer: It was originally the anti-nuclear emblem, invented by request of Lord Bertrand Russell, head of the British Campaign for Nuclear Disarmament (CDN). In 1958, it was designed by Gerald Holtom, a member of the CDN, for a demonstration against a nuclear research center at Aldermaston.
The design comes from the naval flag semaphores for N and D:

Source: Design Boom
The More You Know: In another version of the origin, Holtom wrote:
I was in despair. Deep despair. I drew myself: the representative of an individual in despair, with hands palm outstretched outwards and downwards in the manner of Goya's peasant before the firing squad. I formalised the drawing into a line and put a circle round it.

Holtom came to regret the symbolism of despair, as he felt that peace was something to be celebrated. He wanted the symbol to be inverted.