Red flag laws were laws in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 and the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 enacted in the late 19th century, requiring drivers of early automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s to take certain safety precautions, including waving a red flag in front of the vehicle as a warning.
In the United Kingdom, the Locomotive Acts (also known as Red Flag Laws), a policy requiring self-propelled vehicles to be led by a pedestrian, waving a red flag or carrying a lantern, to warn bystanders of the vehicle's approach.