This badge related to service in the Territorial Force and was introduced by Army Orders in 1910.
It was to be worn on the right breast of the uniform by officers and men who had undertaken the liability to serve outside the United Kingdom in time of emergency under provisions of Section XIII (2)(a) of the Territoral and Reserve Forces Act, 1907. He did so by signing the Imperial Service Obligation.
The badge was a metal tablet 1.625 inches by 0.4 inches in size, with raised lettering reading “Imperial Service” and surmounted by a crown.
Ecah Territorial Force unit that achieved 90% or more of its officers and men undertaking the liability would have the fact recorded alongside its name in the Army List.
It is not possible to directly research the men who were issued with the badge. There are no issuing lists or rolls (at least, that I know of). The signed “Imperial Service Obligation” often appears in a man’s service record, and if he went overseas before March 1916 his acceptance of the liability can be assumed.