A temporary loss of blood flow to the heart causes chest pain, or angina, which is basically a warning sign that something bad could happen shortly.
You might think that the recent financial crisis would have been a warning sign for banks and other financial institutions to back off the metrics and take a more human, holistic approach.
Eleven-year-old Mark Wheeler from California typed out a warning signal using Morse Code.
A colored flare used as a warning signal for trucks and railroad trains.
A colored flare used as a warning signal for trucks and railroad trains
Marking tape can be used as a warning signal on the groud or pillar etc.
Experts regarded it as a warning signal of an economic smashup.