The term "bellwether" comes from middle english. Apparently the Middle Englanders placed a bell around the neck of a castrated Ram. A castrated Ram is a "wether." The flock of sheep would follow the bell toting eunech by listening to the bell ring. In modern usage, bellwether is any presage of a future event.
I read today that the French Anti-doping Agency will cooperate with the USDA's investigation of the former U.S. Postal Cycling Team and Lance Armstrong by providing, if asked, Lance's 1999 blood samples. I think I hear a bell ringing.