Two-Way Traffic Sign
MUTCD W6-3
You are entering a two-way roadway; watch for oncoming traffic.
What it looks like
A yellow diamond warning sign with two black arrows pointing in opposite directions to show two-way traffic ahead.
When you'll see it
You encounter it where a one-way section ends or a divided road becomes two-way, so traffic now flows in both directions.
What to do
Stay in your lane, watch for oncoming vehicles, and do not attempt to pass unless it is clearly safe and permitted.
Related signs
Source: Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition — FHWA.