have pitches that appear to be significantly different. The use of the "fourth chime" ended shortly after the close of World War II. Service Mark registration Prior to 1946, U.S. law limited registered trademarks to tangible goods. The law was changed that year to allow "service marks" for offered services, and, in an application made with the U.S. Patent Office on November 20, 1947, NBC filed for service mark protection for use of its chimes in conjunction with the "broadcasting of radio programs". Notification of the pending application, which stated that the chimes had been in use since November 1927, was published by the Patent Office on January 17, 1950. There were no objections raised, so on April 4, 1950 the three notes of the NBC chimes became an officially registered service mark. It is sometimes incorrectly stated that this was the first grant of a U.S. service mark. Actually, numerous earlier service marks had been approved, but previously they had been logos or descriptive names for the service being provided. What made the NBC chimes grant unique was that this was the first time that a service — in this case NBC's radio broadcasts — was granted protection for the use of a service mark that was a "purely audible" trademark, or what became known as a "sound mark". The original radio broadcasting "sound mark" registration expired on November 3, 1992, after NBC Radio had become a content subsidiary of Westwood One. However, a second registration, made in 1971 and covering the "broadcasting of television programs", remains in force. Later usage Although the Rangertone chime machines had to be manually triggered, in 1950 RCA reported that the chimes now normally "sound automatically at 30 seconds before the hour and 30 seconds before the half hour". A December 1953 report in The Billboard noted that: The use of the chimes as a network communications signal ended around 1971, the result of automation, which in the case of radio led to shorter tones and "chirps" that were commonly filtered out by the stations so they were unheard by listeners, and in the case of television included use of the vertical blanking interval to transmit cues that were not seen by viewers. However, subsequently there have been numerous examples of the chimes being used in NBC programming as an audio signature. In 1974, WNBC incorporated the sequence into the opening of its