San Luis Potosí is, like most current Mexican state flags, the coat of arms centred on a white field.
The flag of the state ofThe coat of arms in divided into two fields, a blue one and a gold one. In the centre, the figure of Saint Louis, King of France, which is also on the top of a hill. On the gold field, there's two gold bars and on the blue field there's two silver bars. It is framed by an irregular golden border.
The coat was given by Viceroy Don Francisco Fernández de la Cueva in 1656 to the then town of San Luis Minas del Potosí of the New Spain along with the title of City and it was officially confirmed by King Philip IV in Madrid in 1658.
Proposals for new flag of San Luis Potosí[]
Blue and yellow for night and day. Two gold and two silver bars which represent the state's mining wealth. By kyrgyzzephyr. 2014.
Inspired in the state's coat of arms, the Flag of San Luis Potosí is composed of San Pedro Hill, and four gold ingots, in the same usage as the coat of arms. By Ricardo Vazoli, 2016.
San Luis Potosí flag proposal by thekeep4223, Apr 2020. (Reddit)