Trivia: The term is "bellwether," i.e. a wether (castrated sheep) wearing a bell, used to guide the flock.
I think that in my mind, it was always some sort of weather related bell, like you ring it, when the weather changes.
Hopefully the sheep reference will help me remember.
I went hiking in Albania recently. I saw many sheep grazing in the mountains. I wondered about the sheep chosen to wear the bell. Like, was it the same sheep every day? Did the chosen sheep think, "Fuck me this thing is annoying"?