As works of the United States government, the images are in the public domain and thus can be used by anyone for any purpose, without licensing issues.
In 1974, the United States Department of Transportation (DOT) recognized the shortcomings of pictograms drawn on an ad hoc basis across the United States Interstate Highway System and commissioned the American Institute of Graphic Arts to produce a comprehensive set of pictograms. In collaboration with Roger Cook and Don Shanosky of Cook and Shanosky Associates, the designers conducted an exhaustive survey of pictograms already in use around the world, which drew from sources as diverse as Tokyo International Airport and the 1972 Olympic Games in Munich. The designers rated these pictograms based on criteria such as their legibility, their international recognizability and their resistance to vandalism. After determining which features were the most successful and appropriate, the designers drew a set of pictograms to represent 34 meanings requested by the DOT.
In 1979, 16 symbols were added, bringing the total to 50.