Emergency Stopping Only Sign
MUTCD R8-7
You may stop along this stretch of road only in an emergency; ordinary stopping, standing, or parking is not allowed.
What it looks like
A vertical white rectangle with black legend reading EMERGENCY STOPPING ONLY in capital letters.
When you'll see it
Posted along freeway shoulders, in tunnels, and on bridges where stopping is restricted except for genuine emergencies.
What to do
You may stop here only in an emergency; ordinary stopping, standing, or parking is not allowed along this stretch.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.