Perfins are a series of small holes in the form of letters or a designs punched in a stamp. The names comes from Perforated Initials . This was an anti-theft procedure in use since in the 19th Century, when a person could bring an unused stamp to a post Office and receive the amount in cash. The key word is "unused". By punching holes in the stamp it become usable only as postage, thus preventing a dishonest clerk from supplementing his income. (Sorry, no Christmas gruel for Tiny Tim).
Mr Joseph Sloper developed a machine in 1868 to punch the holes in a stamp allowing several letters to be punched at one time. Unique designs were also available. These "holey" stamps are quite collectable. Perfins are/were used in more than 214 countries. The British Isles used them extensively, but they can be found used almost everywhere.
The number of holes in a particular letter and the diameter of the holes often vary. For example the letter "M" may have 11,15, 17 or 19 holes depending on the design. Hole diameters are also variable. The layout of the letters may change, in one, two, or three line formats. Spacing of letters can also change. Abbreviations, such as Cº (Company) or Ltd (Limited) may also change.