What are some well known omens?

Well-known omens include a black cat crossing one's path, which is often associated with bad luck, and the appearance of a rainbow, symbolizing hope and good fortune. Breaking a mirror is commonly believed to bring seven years of misfortune. Additionally, the sudden appearance of a crow or a bat is often seen as a sign of impending change or bad news. These omens vary widely across cultures and contexts, influencing beliefs and behaviors.