Hill Sign
MUTCD W7-1
A steep downgrade is ahead; control your speed.
What it looks like
A yellow diamond warning sign with a black symbol of a truck on a downward slope to indicate a steep downgrade ahead.
When you'll see it
It appears at the top of a steep hill or long descent, common on mountain highways and roads with sharp elevation drops.
What to do
Control your speed on the downgrade, shift to a lower gear if needed, and avoid riding your brakes.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.