Founded by Louis Chevrolet and ousted GM founder William C. Durant on November 3, 1911. Chevrolet was positioned by Alfred Sloan to sell a lineup of mainstream vehicles to directly compete against Henry Ford's Model T in the 1920s, with "Chevrolet" or "Chevy" being at times synonymous with GM.
A detailed overview of Chevrolet's history is here. (Note this is a very large pdf file.)
During GM's "Bail Out" these signs started to spring up around Detroit.
A complete collection of the billboards is here.