The US warning sign marking the start of a no-passing zone on a two-lane road is pennant-shaped.
The sign is a distinctive sideways triangular pennant, usually yellow with a black border and black legend. Its unusual shape helps drivers recognize the beginning of a restriction quickly, even before they can read the words. In the federal sign system it is identified as W14-3, the No Passing Zone sign.
The sign is placed on the left side of a two-way road, facing drivers who might otherwise attempt to pass. It commonly appears near hills, curves, bridges or other places where sight distance is too limited for safe overtaking. A separate Do Not Pass sign may also be used on the right side.
The pennant sign does not by itself describe every pavement marking. Drivers must also observe the centerline: a solid yellow line on their side generally indicates that passing is prohibited. The shape is easy to confuse with a diamond, the standard shape for many US warning signs, but no-passing-zone signs are the notable exception.