Correction
Henderson Excelsior
If I May, I'd like to offer a correction. This photois described as being used in our 1923 catalog. In fact, it was not. Further, the lights mounted to the handlebars are just that: lights, not the siren as described. These motorcycles were equipped with a headlight, a spotlight and a red light. The siren is mounted to the left side of the motorcycle and is driven by the rear tire. A small portion of it is visible as a silhouette above the chain guard. The other Mack Sennett photo featuring Elsie Tarron alone was used on the cover of our 1923 Motorcycle Siren Catalog. The siren is actually featured in that photo.
Kevin O'Connell
B&M Siren Manufacturing Co.
Los Angeles

Original description included... the woman in the hat is Elsie Tarron, posing as a police officer writing a ticket.