And then he heard a gut-wrenching sound: the bells signaling an oncoming train.

火车驶来的钟声。

The bell signaled that school was over.

【signal】铃声响起，放学了。

At KT, a telecom company, the sound of that bell signals the end of every work day before the screens go dark.

在AT，一家电信公司，在屏幕变黑之前，这个铃声意味着每天工作的结束。