Similar to a Bellwether, a John Ringer refers to a leading indicator of some sort of change, similar to "canary in a coal mine". Unknown origin, has been used as a common phrase in corporate conference call settings at least going back to the late 90's.
As you can see here on this chart, the strong sales numbers act as a great John Ringer indicating healthy growth.
by hackysackman February 18, 2021