The Vienna Convention on Road Signs and Signals was concluded in 1968.
The United Nations conference in Vienna ran from 7 October to 8 November 1968, and the convention was concluded on 8 November. Its goal was to improve international road travel by bringing national systems of signs, signals, and road markings closer together.
The agreement built on earlier international efforts. A convention on the unification of road signs had been concluded in Geneva in 1931, followed by the 1949 Convention on Road Traffic and a related Protocol on Road Signs and Signals. The 1968 convention updated and expanded that framework for modern international traffic.
Another date often confused with the answer is 1978: that is when the convention entered into force, not when it was concluded. The treaty helped establish widely recognized conventions such as standardized warning symbols, traffic-light meanings, and the inverted triangular give-way sign.