signaling bomb

例句：

1. 1. The military used signaling bombs to mark the border between their two armies.
   军队使用信号弹来标出他们两个军队之间的边界。
2. 2. During World War II, signaling bombs were used to warn of enemy troop movements.
   在第二次世界大战期间，信号弹被用来警告敌方部队的动向。
3. 3. The signalling bomb was a crucial part of the communication system during the war.
   信号弹是战争中通信系统的重要组成部分。