Does the visible sign indicate that you are entering a one-way traffic?

Why?

The round blue C-5 sign means you must proceed straight ahead, as indicated by its arrow. It does not tell you that the road is one-way. A one-way road is indicated by the rectangular D-3 sign, which also has a white arrow on a blue background.

§ 35 ust. 1 pkt 5 i ust. 2 oraz § 44 ust. 1 rozporządzenia w sprawie znaków i sygnałów drogowych