Australia Official Service Perfins
Perfins (perforated insignia) are holes perforated in stamps by both governments and businesses to discourage theft and the improper use of stamps for private purposes. The kangaroo and King George V definitives pictured above are perforated ''OS'' for Official Service by the Australian Government from 1913 to 1931.
The ''OS'' overprint that replaced the perfin is seen on this 1932 issue.
In 1931 the use of an ''OS'' overprint was implemented to replace perfins.
The stamps pictured above are perforated ''G NSW''
for the Government of the state of New South Wales.