Does the visible prohibition sign forbid you from turning left at the intersection?

In the photo you are driving along a wide street in a city behind a dark car and approaching a junction with traffic lights; the traffic lights show green, and sign B-23 "no U-turn" is hanging on a post by the road. This sign does not prohibit turning left - it prohibits only U-turns. The answer is: no.

The Regulation on road signs and signals states that sign B-23 "no U-turn" prohibits drivers from making a U-turn up to and including the nearest junction, and a left turn is prohibited by a different sign - B-21, which also covers U-turns. So the relationship works only one way: a ban on turning left includes a ban on U-turns, but a ban on U-turns does not include a ban on turning left. A U-turn on a busy main road blocks the junction for a long time and surprises oncoming drivers, which is why it is sometimes prohibited where an ordinary left turn is safe. If you want to turn left, you get into the correct lane, switch on your indicator and turn on green, giving way to oncoming vehicles going straight on or turning right.

Legal basis: § 22 para. 1 and 5 of the Regulation on road signs and signals; Art. 25 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)