bellwether

1. (figuratively) Anything that indicates future trends.Examples: "Mortgage delinquencies often act as a bellwether for a forthcoming recession."; "At Hampton Court the little flocks of visitors are not provided with an official bellwether, but are left to browse at discretion upon the local antiquities."; "I suspect that, after all,[…]—that all this has been known, perhaps for ages, to certain ones upon this earth, a cult or order, members of which function like bellwethers to the rest of us, or as superior slaves or overseers, directing us in accordance with instructions received—from Somewhere else—in our mysterious usefulness."Synonyms: gauge, indicator, signfiguratively

2. (finance, figuratively) A stock or bond that is widely believed to be an indicator of the overall market's condition.Examples: "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."figuratively