In the presented situation, can you turn left at the visible intersection?

In the photo, you are driving along a street in a town and approaching a junction; on the right there is a blue round sign with a white arrow pointing up - C-5 "go straight on"; cars are coming from the opposite direction. You cannot turn left at this junction. The answer is: no.

The Regulation on road signs and signals states that mandatory signs C-1 to C-11 require the driver to move in the direction shown by the arrows and apply at the nearest junction or at a place where it is possible to change direction. Sign C-5 "go straight on" only allows you to go straight on - it rules out a left turn, a right turn and a U-turn at this junction. This mandatory sign is equivalent to bans on turning in both directions, only expressed with one sign; turning left despite the sign is a petty offence, and often also means entering a one-way road against the traffic, because road authorities put up C-5 for reasons like this. If you want to get to the street on the left, you go straight on and look for another junction where turning is allowed. The sign applies to the nearest junction - beyond it you may turn again as the signs allow.

Legal basis: § 35 para. 1 and 2 of the Regulation on road signs and signals