Perfin

From StampWantsWiki

Stamps with holes in them that look like initials, company logos or letters, are referred to as PERFINS, (for Perforated Initials). Different companies or organizations used to perforate the postage they had with a company logo or set of initials to show that the postage used was from their company. Some Governments also did this, for other control reasons, and these are considered Official Perfins. The main purpose of these (started with the Oxford Union Society in England in the 1850's) was to control the loss of postage from an organization as postage stamps grew in popularity on letters mailed. They didn't want employees or association members pinching a few dozen stamps for their own use, when they were generally being provided for free to use for company/business mail.