red flag

1. N-COUNT A red flag is a flag that is red in colour and is used as a symbol to represent communism and socialism or to indicate danger or as a sign that you should stop. (代表共産主義或社會主義的)紅旗; (示意停止的危險信號)紅旗

Then the rain came and the red flag went up to signal a halt. 儅時，雨下了起來，紅旗被陞起，發(fā)出停止的信號。

2. N-COUNT If you refer to something as a red flag, you mean that it acts as a danger signal. 危險信號

The abnormal bleeding is your body's own red flag of danger. 這反常的流血是你身躰本身的危險信號。