A sign or omen that precedes an event; a precursor or premonition indicating that something (often undesirable) may happen.
地震の前兆として小さな揺れが続いた。
Small tremors continued as a precursor to the earthquake.
彼の冷たい態度は別れの前兆だったのかもしれない。
His cold attitude might have been a sign that the breakup was coming.
病気の前兆に気づいたら早めに受診しよう。
If you notice early signs of illness, see a doctor promptly.