Road signs, Agricultural vehicles
What does a triangle showing a tractor mean?
Slow agricultural vehicles, such as tractors, are likely to be in the road.

A red-bordered triangle showing a tractor.
What you must do
Be ready to slow down and hold back; they move slowly and may turn into fields.
Where you will see it
On rural roads near farms.
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.