warning sign

plural warning signs

1. A sign that indicates a danger, for example to vehicles on a road or of hazardous chemicals.
2. figurativelyAn indication that someone or something is in danger or at risk.

   it is crucial to recognize warning signs of an impending stroke and to get to a hospital quickly for emergency medical intervention.

   1994, Florence Weiner, Mathew H. M. Lee, Harriet Bell, Recovering at Home After a Stroke: A Practical Guide for You and Your Family

   1 more example

   If Musk’s tweet doesn’t raise bright red warning signs all over the world about his judgment and character, just days after he took over one of the planet’s largest and most influential media machines, I don’t know what will.

   2022 October 31, Robert Reich, “Elon Musk’s Paul Pelosi tweet proves he has no business running Twitter”, in The Guardian, archived from the original on 26 Nov 2022