TrafFix Devices, Inc. v. Marketing Displays, Inc.

After MDI's (plaintiff) utility patents for a dual-spring wind-resistant road-sign design expired, TrafFix (defendant) began selling reverse-engineered signs using the identical mechanism; MDI sued for trade dress infringement, and while the district court found the design functional and thus unprotectable, the court of appeals reversed, holding functionality only bars trade dress protection where it would impose more than a mere reputational disadvantage on competitors.