A signal; anything that indicates, or is characteristic of, the presence of something else, especially of something undesirable.
A perceived change in some function, sensation or appearance of a person that indicates a disease or disorder, such as fever, headache or rash; strictly, a symptom is felt or experienced by the patient, while a sign can be detected by an observer.
Something spoken or written that is intended to warn.
The action of the verb warn; an instance of warning someone.
Used to warn of danger in signs and notices.