The phrase "early warning" is commonly used to describe a signal or indication of potential danger or threat. There are several synonyms that can be used in place of this phrase, including "advance notice," "precautionary measure," "cautionary signal," and "forecasting sign." These terms all convey a sense of awareness and readiness for potential risks or hazards. Other possible synonyms for "early warning" might include "alert," "warning sign," "indicator," or "prophylactic measure." Regardless of the specific phrasing used, the concept of timely notice and preparedness is key to avoiding or mitigating negative outcomes.