The number on a brass On War Service 1915 badge is likely an individual identification number assigned to track the distribution and use of the badge. The code could be a manufacturer's identifier or a reference number for administrative purposes.
The list I have shows a Colt new service with that serial number as being made in 1915.
In the King's Service - 1915 was released on: USA: 16 August 1915
On Secret Service - 1915 was released on: USA: 5 November 1915
The Girl of the Secret Service - 1915 was released on: USA: 2 February 1915
Elman Service was born on 1915-05-18.
Texas Forest Service was created in 1915.
The number 1915 can be a noun, or an adjective enumerating another noun. The year 1915 AD is a noun.
Hellenic Naval Air Service was created in 1915.
Alabama Public Service Commission was created in 1915.
The cast of The Girl of the Secret Service - 1915 includes: Grace Cunard as Barbara Ward Francis Ford as Francis Gordon
Train Order Number Forty-Five - 1915 was released on: USA: 28 August 1915
The cast of On Secret Service - 1915 includes: Edward Coxen as Frank Ketchell George Field as James Whitmore Charles Newton as Marshal Bertram