special signals

例句：

1. 1.Special signals are used to indicate the presence of a particular person or object.
   特殊信号用于指示特定人物或物体的存在。
2. 2. In military communications, special signals are crucial for maintaining communication with allies.
   在军事通信中，特殊信号对于与盟友保持通信至关重要。
3. 3.The police received special signals from the dispatcher indicating a high-risk situation.
   警方从调度员那里收到了特殊信号，表明存在高风险情况。