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How Are Stamps Marked?

Since U.S. postage stamps were first issued in 1847, the post office, the postal service, and private postal patrons, have employed a variety of special markings on some of the stamps which have been issued. Some were developed to prevent stamp counterfeiting, others were used to deter stamp theft, or help solve crimes. Some stamp markings are quite common, others are rare. Some are invisible to the naked eye, while others are prominently displayed on the surface of the paper, or within the paper itself.

Denomination
- An Abraham Lincoln 4c definitive stamp
  
  Every postage stamp is marked with its denomination. On some, it is expressed with both a number and letters, as in "3 cents," or "4c." On higher denomination stamps, the amount may be expressed as "$5." For others, the denomination may be expressed in words as in "two cents." Some stamps simply carry numerical denominations, such as "41," (41-cents). And some use an alphabet letter to denote their denomination. This usually occurs if there is a sudden rate change and the postal service must scramble make stamps available. The "A," and "B" definitives are good examples.
Perfins
- As a way to prevent stamp theft, many private companies used to perforate the center of their postage stamps with a series of initials representing their company name. Collectively, these stamps are known as perfins (perforated initials). Many stamp collectors make collecting the hundreds of perfins that were produced their collecting specialty. Some perfins are extremely rare, and thus quite valuable.
Precanceling
- As a method of improving productivity, the post office and the postal service have both issued precanceled stamps, which eliminated the need to cancel them once they are affixed to a letter. Like perfin aficionados, many collectors specialize in accumulating only precanceled stamps. As postal routing, sorting, and canceling have become largely computerized, precanceled stamps are generally a thing of the past.
Overprints
- During the 1920s, a series of midwestern post office robberies prompted the U.S. Post Office and the Bureau of Engraving and Printing to overprint the then-current series of definitive stamps with either the abbreviation "Kans." or "Nebr." It was thought that this action would assist law enforcement in tracking the stolen stamps back to the criminals. A complete set of Kansas-Nebraska overprints is something many U.S. stamp collectors strive to accumulate.
Watermarks
- As another method of deterring stamp counterfeiting, the U.S. Post Office also printed stamps on watermarked paper. Pressing the still wet paper intended to be used for stamps against a fine wire grid created a shallow impression in the paper. If they were held up to the light, or immersed in a watermark detector filled with carbon tetrachloride (CCl4), the markings were clearly visible. Much like precanceled stamps, watermarked stamps are no longer produced by the postal service.

Stamp Collecting