From The Art and Popular Culture Encyclopedia
The circle-A is almost certainly the best-known present-day symbol for anarchy. It is a monogram that consists of the capital letter "A" surrounded by the capital letter "O". The letter "A" is derived from the first letter of "anarchy" or "anarchism" in most European languages and is the same in both Latin and Cyrillic scripts. The "O" stands for order and together they stand for "society seeks order in anarchy" ("la société cherche l'ordre dans l'anarchie"), a phrase written by Pierre-Joseph Proudhon in his 1840 book What Is Property?.
The circle-A long predates the anarcho-punk movement, which was part of the punk rock movement of the late 1970s. However, the punk movement helped spread the circle-A symbol more widely and helped raise awareness of it among non-anarchists. This process began with the use of anarchist imagery when members of the band Crass became aware of the symbol while traveling through France.
While anarchists have historically largely denied the importance of symbols to political movement, anarchists have embraced certain symbols for their cause, including most prominently the circle-A and the black flag. Since the revival of anarchism at the turn of the 21st-century concurrent with the rise of the anti-globalization movement, anarchist cultural symbols are widely present.