Back when morse was the main means of radio comms, operators used HI to signify they found something funny, sort of an early version of LOL. FB, meant something was good (fine business).
It's not unusual these days to hear old timers actually say both of those phrases during voice comms, even face to face. It sounds ridiculous to those of us that got their licence after the morse requirement was removed, hearing someone saying "hi hi" instead of laughing.