Road signs used by countries in the Americas are significantly influenced by the Manual on Uniform Traffic Control Devices (MUTCD), first released in 1935, reflecting the influence of the United States throughout the region. Other non-American countries using road signs similar to the MUTCD include Australia, Indonesia, Ireland, Japan, Malaysia, New Zealand, and Thailand. They, along with the US Virgin Islands, are also the only countries listed here which drive on the left—with the exception of Liberia and the Philippines, both of which drive on the right.

The Manual on Uniform Traffic Control Devices for Streets and Highways is a document issued by the Federal Highway Administration (FHWA) of the United States Department of Transportation (USDOT) to specify the standards by which traffic signs, road surface markings, and signals are designed, installed, and used. In the United States, all traffic control devices must legally conform to these standards. The manual is used by state and local agencies as well as private construction firms to ensure that the traffic control devices they use conform to the national standard. While some state agencies have developed their own sets of standards, including their own MUTCDs, these must substantially conform to the federal MUTCD.