signal for stub-end track

例句：

1. 1. The policemansignaled the driver to stop.
   警察示意司机停车。
2. 2. The traffic light is signaling thatit's time to turn.
   交通灯正在提示我们该转弯了。
3. 3. The pilotsignaled for emergency landing.
   飞行员发出了紧急着陆的信号。