According to call sign reference data “HL” is one prefix of a ham radio call sign in South Korea. There are several others for South Korea also.
Camp Red Cloud South Korea 1967. Operated under some rather strange circumstances I NOT a ham radio aficionado fully understood. It was an old MARS station that wasn’t authorized under that ticket anymore, but was able to operate low wattage locally, BUT our AR guy had a little Collins kicker down below the desk that apparently in conjunction with the old MARS antennae array allowed us Worldwide communications.
I assisted the amateur radio operator at the time during the Christmas phone patches so our guys could talk to their families. It was fun, and interesting. I’m amazed I can remember the call sign actually.