Reverse Turn Sign
MUTCD W1-3R
A sharp turn one way then the other is ahead; slow down.
What it looks like
A yellow diamond warning sign with a black arrow that bends first one way and then the other, showing a reverse turn.
When you'll see it
It appears before two sharp turns in opposite directions that follow closely together, common on winding rural and hillside roads.
What to do
Slow down before the first turn and stay at a controlled speed through both bends, keeping to your lane.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.