What's the difference between water injection road flag and water injection knife flag?

Street signs generally refer to advertisements on street lamps, which are on both sides. Water-filled signboards are solid bases filled with water;

Knife flag, as its name implies, refers to a flag shaped like a knife, usually with only one side. The symbol of the water injection knife is that the base is stable in water injection.

Basically, there is not much difference. One is a flag and the other is two flags.