The purpose of a red flag is to alert people. It is a warning sign that indicates danger or a potential problem. Red flags are often used in situations where there is a risk of harm or injury, such as in hazardous work environments or when dealing with hazardous materials. They can also be used to indicate a potential security threat or to warn of an impending natural disaster. Red flags are also used to signal the need for caution or to draw attention to a particular issue.