The phrase "sign things to come" is often used to describe something that foreshadows a future event or trend. There are several synonyms that can be used interchangeably with this phrase, including "harbinger," "omen," "portent," and "predictive." A harbinger is something that indicates the approach of something, typically something undesirable. An omen is a sign that something good or bad is likely to happen. A portent is a warning sign of something significant or calamitous about to happen. And predictive is something that foretells the future course of events. All of these synonyms capture the idea of something indicating a future event, making them useful for writers, analysts, and anyone looking to discuss future possibilities.