Sentence examples for black flag from inspiring English sources

The phrase "black flag" is correct and usable in written English.
It can be used as a noun phrase to describe a specific type of flag that is black in color. It can also be used as a metaphor to represent something negative or threatening. Example: The pirates raised the black flag, signaling their intention to attack the merchant ship. Example: The company's falling profits were a black flag, indicating potential financial trouble.