Riggs conceived of the concept while employed as a state trooper, attending Chicago's Northwestern Traffic Institute in 1939, and developed the idea further over the next decade. One of the class discussions concerned a common problem of motorists rolling through an uncontrolled intersection and the fact that police were reluctant to issue a traffic ticket. Riggs continued to think about the problem. His goal was to create a sign that would both control traffic at an intersection, but affix civil liability for a driver that failed to yield.