Cinco De Mayo is the Mexican national holiday widely celebrated by Mexican Americans in United States on May 5th in remembrance of the 1862 Battle of Puebla.
The poster below, courtesy of the Royal Chicano Air Force Archives collection, part of Opening History aggregation, shows an announcement for celebration of Cinco De Mayo in California. The second item featured here, courtesy of Galeria de la Raza Archives – Catalog of Slides collection, is a photograph taken at 1977 Cinco de Mayo Parade.