Originally intended for the entire country, the flag became the de facto symbol of São Paulo after the constitutionalist revolution, but was only adopted officially in 1946 after the federal constitution gave states and municipalities the right to create their own symbols.
The flag has thirteen stripes alternating between black and white, representing the days and nights that the bandeirantes fought for the good of the state.The top and bottom stripes are both black, so the edges are clearly delimited.
The canton consists of a red rectangle on the upper left corner, representing the blood shed by the bandeirantes. The white circle contains an outline of Brazil in blue, the color of strength, which the bandeirantes brought to the state. There is a yellow star on the inside of each corner of the rectangle.
According to its designer, the writer Júlio Ribeiro, the colors of his proposed republican flag, which later became the state flag, were chosen for five reasons: (1) the sharp contrast of the black and white and the harmony of both colors with red; (2) the existence of colorfast dyes in these colors, making for a durable flag; (3) the flag’s compliance with heraldic rules, especially the law of tinctures; (4) its novelty—it had no ties to any of the country’s imperial symbols; (5) the appropriateness of the colors as representing the synthesis of the European (white), African (black), and indigenous (red) peoples into a single Brazilian nationality. He said the stars on the canton represented the four major stars of the constellation of the Southern Cross (Cruzeiro do Sul) and in fact nicknamed his flag the “black and white banner of the Cross (alvo-negro pendão do Cruzeiro).”
On 20 September 1922, however, the São Paulo newspaper Correio Paulistano, referring to “a flag that use and custom hallow as that of São Paulo,” said the flag represents that at any time of night or day (black and white) the people of São Paulo stand ready to shed their blood (red canton) in defense of Brazil (map) at all four cardinal points of the compass (four stars). This explanation is what was written into the law adopting the flag officially in 1948, and is therefore the official statement of the symbolism of the flag—although it is clearly not what the designer intended.