bellwether
/ˈbelˌweðə(r)/noun
1- the leading sheep of a flock, with a bell on its neck（走在羊群前头的）系铃领头羊。
1.1
- an indicator or predictor of something标志, 征兆, 预示：
Basildon is now the bellwether of Britain's voting behaviour.
巴西尔顿成了英国投票行为的风向标。