its challenged articles are not "unpatented" [as required for a false marking claim] because they practice a once-existing, but now-expired, patent.
The Court explained that the Federal Circuit's Forest Group, Inc. v. Bon Tool, Co. decision addressed this question:
All of those perceived evils [i.e. allowing the public to rely on marking, dissuading competitors from entering the market, deterring scientific research] are present when a patentee continues to affix the "patent" designation to an article even after it has entered the public domain by reason of the patent's expiration.
Most notable for me was the Court's introductory paragraph -- it does not seem happy:
Stanley Black & Decker, Inc has noticed up for presentment on May 14 a motion to dismiss this action brought against it by Zojo Solutions, Inc. -- an action among the very large number of lawsuits around the country that claim false patent marking in violation of 35 U.S.C. 292(a). This and all such other actions, which dot the greensward of patent litigation like an infestation of dandelions, have been prompted by the Federal Circuit's decision in [Forest Group] which has created the prospect of extraordinarily large damage awards in qui tam suits brought to enforce Sectino 292(a).