In the case of Traffix Devices, Inc. v. Marketing Displays, Inc., 2000, the U.S Supreme Court ruled that a design patent's expiration leaves it in public domain and thus unprotected by trademark law. The dispute arose when Marketing Displays accused Traffix Devices of infringing on its dual-spring sign stand design which had been patented but was now expired. While Marketing Displays argued that their product’s appearance had acquired secondary meaning (a key requirement for trade dress protection), making it eligible for trademark protection even after patent expiry, the court disagreed stating there was no evidence to support this claim. The court further clarified that if a product feature is functional or essential to use then it cannot be protected under trade dress laws as doing so would hinder competition - an outcome contrary to the objectives of patent law.

In the dissenting opinion for Traffix Devices, Inc. v. Marketing Displays, Inc., it was argued that a product's design could be protected under trademark law even if its utility patent had expired. The dissenting justices believed that the majority ruling undermined the Lanham Act’s protection of trade dress by making it subservient to patent law and ignoring whether consumers associated a particular feature with a single producer or source - which is key in determining distinctiveness necessary for trade dress protection. They pointed out that there are many instances where functional elements also serve as strong brand identifiers (e.g., Coca-Cola bottle shape). Therefore, they contended that just because an element has some functional aspect does not mean it cannot simultaneously serve as an identifier of source – thus deserving trade dress protection.