In late 1919, the National Radio Company received experimental licences for three San Francisco radio stations -- the Fairmont Hotel station was issued 6XG as its callsign.
 
San Jose Evening News, February 17, 1920, page 3:

LOCAL  LAD  PUTS  OVER  GREAT  TEST  OF  RADIO  PHONE
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    The fact that the apparatus used in the following tests was constructed by Emile Portal, a San Jose boy widely known here and a former student the San Jose high school, gives the story a strong local interest.
    Emile Portal is now one of the principal engineers of the National Radio company and has conducted many experiments with amplifiers, designing some which reproduce European wireless messages loudly enough to be heard 100 feet from the apparatus. Portal will leave shortly for Victoria, Vancouver and Seattle to construct radio telephones for his company.
    At 10:30 in the evening the big naval radio station at Mare island, filliped a message on to the drumming night air that brought every operator up in his seat within a radius of 2000 miles.
    "BK-BK-BK-all-stns NPH!" whined the high frequency oscillations.
    Translated from the code of the air into common phraseography, the letters meant: "Break, break, all stations by order of Mare Island."
    An imperative order, preceded by "BK," means but one thing to the radio men--an SOS or distress signal, or an emergency call faint and far distant, out somewhere on the watery wastes where only the pulsing currents of the delicate receiving audions can hear the whispers.
    Station after station halted the business. Boat after boat shut off its generators, while scores of operators humped over their instruments and listened, tuning feverously. Finally from far off Bremerton navy yard came a query:
    "What do you hear?" it asked.
    "BK-break for radio-telephone test," snapped back Mare Island over 1000 miles of land and water. Bremerton subsided.
    And then, clear and sharp on the air, like the sound heard through a suddenly opened door, came the sound of music. It was the lilt of an orchestra, the swinging, rhythmic, pulsing music of a two-step. Battleships cruising days off shore heard it. Fishing boats and merchant craft crawling from Arctic expanses heard it. The operator at the lonely station at Point Loma heard it. And far down among the white-caps of Magdalena Bay a freighter heard it.
    But that was not the miracle. The real accomplishment was at the Oakland auditorium. The orchestra was playing in the palm room of the Fairmont hotel in San Francisco. Through generators, oscillators and reproducers the strains of the orchestra picked up by a big horn were transformed into pulsing radio currents. There were led to the copper filaments of the antennae that swung on the roof of the hotel.
    Across the bay were the strains of music in radio notes. Wires on the roof of the Oakland auditorium picked them up. Down below they were again transformed into mechanical sounds--the reproduced sounds of the Fairmont orchestra. Into big horns hung high in the auditorium went the impulses. And on the floor 5000 people, members of the American Legion and their guests, danced the mazes of the two-step to the music played in the palm room of the Fairmont hotel.