The correct answer in the official bank: 30 k.p.h.
The sign marks a shared street, where pedestrians, including children, share the road with vehicles. The maximum permitted speed within it is 30 k.p.h., so drive slowly and be ready to stop. Speeds such as 50 or 60 k.p.h. are too high for such an environment.
Topic: Traffic signs. The bank marks it for these classes: Light truck (C1), Heavy truck (C), Bus (D), Motorcycle (A), Tractor (1), Private car (B).