Marking a product with a patent number is circumstantial evidence (in the form of any other “extrajudicial admission”) that weighs in favor of finding infringement, but true “marking estoppel” does not apply. The accused infringer is free to introduce counter evidence or explanation.
Background / Facts: The patent here covers certain tennis racket designs and has been licensed by Wilson from Mr. Frolow, who believes that Wilson has not paid him adequate royalties by refusing to recognize certain racket models as falling under the “Licensed Products” of the license agreement. This is despite the fact that Wilson marked several rackets with the corresponding patent number, which Wilson now asserts was done by mistake. In dispatching the case on summary judgment in favor of Wilson, the district court noted test data provided by Wilson that purported to show that the racket models had a moment of inertia of eighty ounce-inches squared or less, thus falling outside of the scope of the asserted claims, and went on to conclude that Wilson’s marking had “no bearing on whether literal or doctrine of equivalents infringement has occurred.”
Issue(s): Whether marking a product with a patent number can be used as evidence of literal or doctrine of equivalents infringement.
Holding(s): Yes. The court refused to adopt the doctrine of “marking estoppel” recognized in some circuits, where a party that marks its product with a patent number is estopped from asserting that the product is not covered by the patent. However, it agreed that the fact that Wilson marked their products with the patent number is a cognizable fact that supports the allegation that Wilson’s products fall within the patent claims. The court likened this fact to simply a form of “extrajudicial admission” that the product falls within the patent claims. “Generally, extrajudicial admissions of facts, such as patent marking, are simply evidence that may be countered by the party that made the admission. These admissions are not binding, and may be controverted or explained by the party that made the statement. … The act of marking is akin to a corporate officer admitting in a letter or at a deposition that the company’s product infringes a patent. A defendant, of course, is free to introduce counter evidence or explanation.”