信号枪

例句：

1. 1. The policeman used his hand as a signal to stop the car.
   警察用手势示意停车。
2. 2. The traffic light is a common signal for pedestrians to cross the street.
   交通灯是行人过马路的常见信号。
3. 3. The pilot signaled the plane to land at the airport.
   飞行员向飞机发出降落的信号。