The fast blue one.

Chief Richard Holme is riding is a Henderson Deluxe. The 1922 Henderson Deluxe had a four cylinder engine of 79.4 cubic inches that put out 28 horsepower. There was a famous race between Henderson and Harley Davidson in which the Henderson won eleven out of the 12 races. Afterwards police departments all across America were ordering these Henderson Deluxe motorcycles, which became, known as "the fast blue ones". The stock Henderson Deluxe motorcycle could hit one hundred miles an hour. In 1924 a Henderson hit 127 mph in the quarter mile.

Via: The Holme family