Portentous signs are OMENS that are seen as a warning of something important or significant. They are often seen as a sign of impending danger or disaster, and can be interpreted in many different ways. In some cultures, portentous signs are believed to be messages from the gods or other supernatural forces. In other cultures, they are seen as a sign of fate or destiny. Regardless of how they are interpreted, portentous signs are seen as a warning of something important or significant.