During the 1940s, the LAPD began alerting radio reporter Loyd Sigmon whenever a major automobile accident occurred on city streets. These notices became known as "SigAlerts," and were later issued to alert all local media. The term "SigAlert" eventually came to apply to any incident on greater Los Angeles area freeways which block two or more lanes of traffic for two or more hours.
For more information on Loyd Sigmon and SigAlerts, visit Harry Marnell's web site SIGALERT!
From a Los Angeles radio DJ reporting on traffic: “The 605, that demon freeway, ought to be called the 666!”