Road Signage A38/A385

I noted a recently replaced road sign (28/6/22) at the A38/A385 junction near South Brent – “Dartmoor – Which roads are suitable”. The sign shows the different classes of roads (Black – Most Vehicles | Blue – Medium Vehicles | Brown – Light Vehicles | White – Local traffic).

Can you tell me the location of any similar signs explaining the road code colour system?

This is the last remaining sign in place in Devon.