2.25" with no back paper and no maker name. Surface has about a half dozen hairline scratches some about 1.5" long but mostly just showing in reflected light. Top center has near pinpoint dot of missing cello showing as a tiny white mark. Button is from the very early years of the sport with road racing beginning as The Long Island, New York Road Race (held 1904-1910) followed by a similar road course race in Savannah Georgia that existed 1908-1911. The Santa Monica Road Race began in 1909 and continued through 1919. The 1912 race represented by this button saw a new group take over the Santa Monica Road Race offering a $5,000 purse which drew some of the best race car drivers in the country. The race was won by Tetzlaff with a speed of 78.718 mph. A very limited issue to event workers only and the first we've seen.