Bellwether

しるし

shirushi

(anything that indicates future trends)

兆し

kizashi

(anything that indicates future trends)

兆候

chōkō

(anything that indicates future trends)

前触れ

maebure

(anything that indicates future trends)

指標

shihyō

(a stock or bond that is widely believed to be an indicator of the overall market's condition)

鈴つき羊

suzu tsuki hitsuji

(the leading sheep of a flock, having a bell hung round its neck)