Do Not Enter Sign
MUTCD R5-1
Do not enter the roadway in this direction.
What it looks like
A red circle containing a horizontal white bar, with the words DO NOT ENTER in white on a white square background.
When you'll see it
Posted at freeway exit ramps, one-way street exits, and driveways to warn against entering a roadway from the wrong direction.
What to do
You must not enter the roadway in this direction; find the correct entrance and approach with traffic flow.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.