What weather sign is this?

This is a sign of "sandstorm weather"

It refers to a severe sandstorm weather phenomenon in which strong winds blow up and drag a large amount of sand and dust on the ground into the air, making the air particularly turbid and the horizontal visibility less than one kilometer.

Postscript (same as postscript); Police officer (police sergeant)

Relevant meteorological symbols: S is floating dust weather, and the vertical arrow in the middle of S is sand blowing weather.

The arrow to the right in the middle of S indicates sandstorm weather, and the double arrow to the right in the middle of S indicates strong sandstorm weather.