Dispatch riders: The Canadian Signal Corps.

Inglis Sheldon-Williams "Motorcycle courier, Canadian Signal Corps, 1917".

Via: cmh

"In the days before portable and reliable radio sets, motorcycle couriers (or 'dispatch riders') were often the fastest way of moving messages to and from the battlefield, especially when laying telephone or telegraph lines was impossible. This 1917 painting of a courier with his mechanical mount is by Inglis Sheldon-Williams, an official Canadian war artist. Note the white over blue badge on this man's arm. When the first motorcycle dispatch riders were introduced, they wore a blue/white brassard on their arm. The colour combination was used for signal flags, and was distinctive enough help give dispatch riders priority on the roads".