Which road sign indicates that turning around is not allowed?

Your answer is correct because all the indicated signs (1, 2, and 3) forbid or relate to turning around in different ways:

- Sign 1 (a red circle with a U-turn arrow crossed out) explicitly means "No U-turn," directly forbidding turning around.
- Sign 2 shows the start of a motorway (blue sign with road symbol). On motorways, U-turns or turning around is prohibited for safety reasons.
- Sign 3 indicates a tunnel entrance. In tunnels, turning around is also forbidden due to high risk caused by limited space and visibility.

In German traffic rules, these signs help prevent dangerous maneuvers like turning around in places where visibility or space is limited, or where such actions could disrupt fast-moving traffic. Understanding these signs helps you know where it is safe and legal to make a U-turn and where it is prohibited for safety reasons.