I was gifted with a great vivid memory and I use them in my stories. I was 17 and a friend asked me to ride along in his cab for fun. I don’t know if it’s universal, but his calls were “bells” and he would get as many as three “bells” or passengers waiting for pick up. At the time, there were competing companies who were stealing dispatch messages and sending their drivers out to pick up another companies “bells”. It was a huge deal. Loved remembering those fun ride-alongs.