What maneuver does this regulatory sign prohibit?

Correct answer: B – Making a U-turn
This is a No U-Turn sign. It prohibits turning the vehicle around to travel in the opposite direction at the location where the restriction applies. It does not prohibit every type of turn or indicate that the roadway is one-way.
Source: Manual on Uniform Traffic Control Devices for Streets and Highways, 11th Edition with Revision 1 — Ch. 2B, “Movement Prohibition Signs (R3-1 through R3-4, R3-18, and R3-27)”

