Perfins is an abbreviation for “perforated initials” or “perforated insignia.”
Perfins are holes added to stamps for special reasons, and can make an interesting collection. A perfin is a perforated design, symbol, insignia, letter, or group of letters in a postage stamp placed there by an individual, organization, or government agency for the purpose of preventing unauthorized use.
In earlier times, stamps often functioned as money in small transactions. In Great Britain, where the idea of perfins was invented, post offices would redeem stamps for cash, if the trade-ins were in pairs or larger multiples. Employees who took stamps from the office could sell them back to the post office or to other businesses as postage, use them themselves as postage, or offer them in lieu of cash for goods. Stamps with perfins became identifiable, not negotiable outside the office mailroom.
Postage meters were invented in the 1920s and replaced perfins in many offices, but perfins continue to be used today throughout the world.
Mounting perfin stamps on a black background can help to make the pattern of holes more obvious. It also may be helpful to mount the stamp design-side down, on a black background. This will show off the perforated initials so that they easily can be read.
Examine the perfins, and if the stamp was originally punched from the front of the stamp, rather than the back, it may be helpful to mount the stamp face side up. Otherwise, you may want to mount them with the face side down for easier identification.
It is a fascinating part of stamp collecting with easy-to-find and mostly inexpensive material.