Road signs, No buses
What does a red ring with a bus mean?
No buses or coaches with more than 8 passenger seats.

A white circle with a red border and a bus.
What you must do
Do not enter if you are driving a bus or coach of this size.
Where you will see it
On roads unsuitable for large passenger vehicles.
Test yourself
The theory test asks you to recognise signs like this one. Try the road and traffic signs short test (with an easy and a hard set), or read the signs revision notes. Source: Know Your Traffic Signs.
Other common road signs
Meaning based on Know Your Traffic Signs and The Highway Code. The sign image is an official Department for Transport sign (Crown copyright) from Wikimedia Commons, reused under the Open Government Licence or the public domain. Always check the current Highway Code on gov.uk. Not affiliated with or endorsed by the DVSA.