red flag

figuratively US idiomatic

(figuratively) A cue, warning, or alert; a sign or signal that something is wrong. / (idiomatic, US) red rag

Japanese Meaning

警告のサイン / 注意を促す兆候 / 警告信号 / 問題が発生する可能性を示す兆候

When he contradicted every fact and refused to apologize, it was a clear red flag in our partnership.

彼があらゆる事実に反論し、謝罪を拒んだとき、それは私たちの関係における明らかな警告サインだった。

Sense（1）

(figuratively) A cue, warning, or alert; a sign or signal that something is wrong.

Improper formatting is a red flag to look for other problems with the data.

Sense（2）

(idiomatic, US) red rag

Sense（3）

Sense（4）

(politics) A common symbol, usually in the form of a banner, for leftist revolutionary ideologies, especially socialism.

red flags

（ plural ）