The Motor Car Acts of 1896 and 1903 introduced signage to warn of the weakness of bridges constructed in the 18th and 19th centuries. These were built when traffic was light and there were fears they were not strong enough to withstand heavier vehicles such as buses and goods transport.

The article notes that 'Experience has shown, however, that the vast majority of these so-called "weak" bridges have proved capable of carrying without visible ill-effects much heavier vehicular traffic ... than was ever contemplated.' The article rumbles on in detail about construction techniques and later Acts - a Google on 'notice this bridge is insufficient' will turn up this article for you to read at leisure.

The sign reads
NOTICE
This
BRIDGE
is insufficient to carry a
HEAVY MOTORCAR
The Registered Axle Weight of any axle of which exceeds
THREE TONS
or the Registered Axle Weights of the
several axles of which exceed in the aggregate
FIVE TONS
or a Heavy Motor Car drawing a
TRAILER
if the registered Axle Weights of the several axles
of the HEAVY MOTORCAR and the
Axle Weights of the several Axles of the
TRAILER
Exceed in the aggregate
FIVE TONS

The use of capitals and lowercase is eccentric and perhaps not easy to read at speed , but it would not be easy to miss the sign.