What’s the meaning of this sign?

Explanation: This sign tells you that the minimum permitted speed is 30 mph. Signs like this are put in place to keep traffic flowing, and ward off vehicles that can't go faster than this. Despite there being a minimum speed limit, you should still stop or slow in the event of a queue, hazard, or collision.

Category: Road and traffic signs (2021)

References: The Official DVSA Guide to Driving: Section 6, Highway Code: Page 107, Know Your Traffic Signs: Page 21