signal line

基本解释

Those buttons usually have lamps and can provide features such as call holding, line status, signaling, conferencing and intercom.
这些键有指示灯并且可以提供诸如电话接听等待、线路状态、信令、会议和连络用对讲电话装置的功能。
wiki.mycreative.com.cn
Considering the signaling system project for Beijing subway Line 4 and its extension, two different implementation options are discussed.
针对北京地铁4号线及其延伸，讨论线路延伸工程中信号系统适用的两种实施方案。
Signaling the line of books that are waiting to be read, it isn't rare to hear him say "Dear God, I'm an imposter, when will people realise I can't read all this?"
他也会划线标记出书中待读的部分，经常就会听到他说“天啊，我就像个江湖骗子，人们什么时候才会知道我还有这么多书需要读啊？”

If you start to cross the line without signaling, it triggers a warning.
FORBES: Cadillac Has A Backseat Driver I Can Live With
The relative performance broke its downtrend, line c, in May signaling the resumption of the major uptrend.
FORBES: Don't Bet Against the Consumer
The RS broke its major downtrend, line a, in April, signaling its market-leading performance in the second quarter.
FORBES: 4 Surviving Sectors