The two-flags Antifa logo is inspired by the original logo of the Antifaschistische Aktion a militant anti-fascist organization in Germany that existed from 1932 to 1933. It remains a widely used symbol of militant anti-fascism. The black flag represents anarchism and the red flag represents communists, both united against fascism.
The colors black and red have been used by anarchists since at least the late 1800s, though generally used by anarcho-communists. The flag was used as the symbol of the anarcho-syndicalists by the CNT during the Spanish Civil War. The black represents anarchism and the red represents leftist and socialist ideals. George Woodcock writes that the bisected black-and-red flag symbolized a uniting of "the spirit of later anarchism with the mass appeal of the First International"