Turn Sign
MUTCD W1-1
A sharp turn in the road is ahead; slow down.
What it looks like
A yellow diamond warning sign with a black arrow bending sharply in one direction to show a tight turn ahead.
When you'll see it
It appears in advance of a sharp bend in the road, common on rural highways, mountain roads, and where a street angles abruptly.
What to do
Slow down before you reach the turn and steer smoothly through the bend, keeping to your lane.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.