From "Wealth of Ideas" e-newsletter, May 2004

Did you ever notice a patent number on a product and wonder why such marking was there? We are accustomed to seeing patent numbers on almost everything, and here's why: by doing so, the patent owner informs the world that the product is patented and thereby puts infringers on notice of the patent rights.

Specifically, placing patent numbers on products (or their packaging, if placement on the product itself is impractical or impossible) is called patent marking and is considered constructive notice. Constructive notice is not a legal requirement, but it is to the patent owner's advantage. (If the patent owner is not practicing the invention at all, there are no products to mark and thus no marking requirement in order to collect damages.)

If a product is produced and sold without patent marking, the owner must resort to actual notice – notifying the infringer(s) of the alleged infringement, usually via a letter. Constructive notice is preferable to actual notice for two reasons: 1) With actual notice, damages only start from the date that notice is given; and 2) A notice letter may expose the patent-holder to the risk of a declaratory judgment action – a pre-emptive strike wherein the infringer actually sues the patent-holder!

The moral of the story is this: If you have a patent, make sure that your products (and your licensees' products) are marked with the patent number. The question of whether or not you mark can have serious consequences for your ability to collect damages.