The Circle-A is known to the public and accepted by anarchists as a traditional symbol for anarchy. It doesn't have such a long history behind it as one might think though, it is actually rather new in the anarchist iconography
The symbol was created in April 1964 in a internal bulletin of the organization Jeunesses Libertaires(Libertarian Youth) i France. The Circle-A was a suggestion as a simple and recognizable graphic symbol for anarchism.
According to the swedish anarchist Gustaf Gimsberg the big A in the ring was an development of the peace symbol, while most hold that the young french anarchists hinted at Pierre-Joseph Prodhoun's famous statement that "Anarchy is order" (hence an A in an O).
The suggestion never really gained popularity. But in 1966 the Sacco and Vanzetti group in Milano started to use it. Until 1968 it's use was limited to Milano, but during the May events in paris 1968 it was seen everywhere - on walls, posters, banners and flags. It quickly spread over the world. The circle-a came to be a symbol directed against the national symbols, the national flags and instead a universal and international symbol for the state- and classless society.