"Perhaps most importantly, consistently marking your products as patented can affect the damages you could recover in the event someone infringes your patent. That is, if you consistently mark your products this puts the world on what is called “Constructive Notice” that your product is patented. That means that any infringer should have known that the product was patented (because the product itself says “Patented”) and therefore the patent owner can get damages starting on the date of infringement. If a patent owner does not mark their products, they can only recover damages for infringement that occurs after the patent owner sends a letter to the infringer informing them of their patent rights."
"The reason is that if products are not appropriately marked before they enter the stream of commerce, the damages that the manufacturer can receive in a patent infringement action against someone that has copied that product are reduced.
35 USC §287(a) provides:
Patentees, and persons making, offering for sale, or selling within the United States any patented article for or under them or importing any patented article into the United States, may give notice to the public that the same is patented, either by fixing thereon the word “patent” or the abbreviation “pat.”, together with the number of the patent, or when, from the character of the article, this cannot be done, by fixing to it, or to the package wherein one or more of there is contained, a label containing a like notice. In the event of failure to so mark, no damages shall be recovered by the patentee in any action for infringement, except on proof that the infringer was notified of the infringement and continued to infringe thereafter, in which event damages may be recovered only for infringement occurring after such notice. Filing of an action for infringement shall constitute such notice."
