What does the navy D flag mean?

The D-flag itself means "Our ship is difficult to steer, please avoid it". Now the joke circulating on the Internet is that no matter what actions our marine police plan to take against Vietnam and the Philippines at sea, they only hang the D-flag, making them look like they can't control the collision and let them suffer dumb losses. In the South China Sea, China's law enforcement vessels hang a D-flag, which means "Our vessel is in difficulty in maneuvering, please avoid it". If there is any action against Vietnam and the Philippines, hang the D-flag and make it look like the ship can't control the collision before it goes, so as to reduce the active collision against international public opinion.