What does the mini-roundabout sign mean?
A mini-roundabout ahead. Give way to traffic from your right and pass round the central markings.

A blue circle with three arrows turning clockwise.
What you must do
Treat it like any roundabout: give way to the right and signal your exit.
Where you will see it
Smaller junctions in towns and residential areas.
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: Highway Code rule 188.
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.