This series served as a nominal index to several series of Investigation  Branch/Security service files over an extended period. In most cases entries refer to individual people but some reference is made to organizations. Many entries are just name and file reference. Others give detail of the case subject. Subjects covered include: aliens, immigration, naturalisation, internment, whereabouts, debtors and bankruptcy, character and security checking, general security inquiries. A small number of cards refer to staff appointments and applicants for vacancies.
 
Some cards note that the file has been destroyed or transferred to ASIO or archives.
 
It is thought that the series was created primarily to control the "SA" files of the Investigation Branch and the "S" and "SS"
references were added in the late 1940's after the abolition of the Security Service.
 
D1902 was relocated from South Australia to the ACT in September 2021.