bellwether

Several old ladies forthwith proclaimed their intention of following him; but, as one or two of them were deaf, and another had been threatened with an attack of that mild, but obstinate complaint, dementia senilis, many thought it was not so much the force of his arguments as a kind of tendency to jump as the bellwether jumps, well known in flocks not included in the Christian fold.

One of my favorite sentiment indicators is bellwether stocks — key stocks that are leaders in their fields. When investors buy or sell these shares, it's usually a good sign of confidence or the lack of it in that sector of the market and sometimes even the economy.