signal

The lighthouse flash is a signal to warn ships that there are rocks nearby.

(Chinese) 灯塔的闪光是警告船只附近有礁石的信号。

The coach gave a hand signal to tell the players to change their strategy.

(Chinese) 教练做了一个手势，示意队员们改变策略。

The traffic light signals to drivers when they should stop or go.

(Chinese) 红绿灯向司机发出何时停或行的信号。

He signaled to the waiter that he was ready to pay the bill.

(Chinese) 他向服务员示意他准备买单了。