Perfins

I have a few stamps with holes in them. These are Perfins. In philately, a perfin is a stamp that has had initials or a name perforated across it to discourage theft. The name is a contraction of perforated initials or perforated insignia. They are also sometimes called SPIFS (Stamps Perforated with Initials of Firms and Societies). You can read more about these here: https://en.wikipedia.org/wiki/Perfin

You can read more about HMSO here: http://www.angelfire.com/pr/perfinsoc/ex/HMSO.pdf