What are perfins and why do stamps have perforated holes?

In philately, a perfin is a stamp that has initials or a name of a company perforated across it to discourage theft of postage stamps.

The name is a contraction of perforated initials or perforated insignia.

They can sometimes be called SPIFS (Stamps Perforated with Initials of Firms and Societies) too.

Great Britain was the first country to use perfins which began in 1868. The practice spread quickly to Belgium (1872); Denmark, France, Germany and Switzerland (1876); and Austria in (1877).

The United States finally allowed perfins in 1908.

Example of a British Machin stamp which was perforated with STH initials:

In some cases collectors may value perforated stamps less but in recent times these stamps have become unique and are quite desirable and may be collected separately. The perfin company origins are also very fun to trace.