The first U.S. Route signs were installed in 1926. They marked the new United States Numbered Highway System, created to give important roads consistent national route numbers and markers.
The U.S. Route shield was developed by the Joint Board on Interstate Highways. Ohio board member Lou A. Boulay is credited with proposing a shield design inspired by the shield on the Great Seal of the United States. The route-numbering plan was approved in 1926, and the earliest signs followed soon afterward.
The original marker was more elaborate than today’s familiar shield. Early versions could include the state name, “U.S.” or “U.S.A.”, and the route number. Later editions simplified the design and standardised typefaces, layouts and sign dimensions.
The date is sometimes confused with later redesigns. The 1948 Manual on Uniform Traffic Control Devices introduced a major revision using FHWA typefaces, while the current shield style dates from the 1971 MUTCD. Those are design milestones, not the beginning of U.S. Route signs.