US road sign R3-4 · regulatory signs
No U-turn
California MUTCD, sign R3-4What does the No U-turn sign mean?
You may not make a U-turn here.
How regulatory signs work
They give a rule you must obey. They are rectangular unless the manual names another shape (California MUTCD, section 2B.02); the STOP sign, for example, is an octagon (California Driver’s Handbook, “Laws and Rules of the Road”).
