In this scenario, are you obliged to bring your vehicle to a stop before the visible prohibition sign?

In the photo you are approaching a level crossing whose barriers are up; on the right there is a round sign with a red border and the words "Rogatka uszkodzona" (barrier out of order) - a version of sign B-32. In this situation you are always obliged to stop the vehicle before this sign. The answer is: yes.

The Regulation on road signs and signals states that sign B-32 "stop - customs control" means an obligation to stop, and instead of the words "Cło-Zoll" (customs) it may carry the words "Rogatka uszkodzona" (barrier out of order), "Sygnalizacja uszkodzona" (signals out of order), "Kontrola drogowa" (road check) and others, depending on the reason for stopping; you should stop at the place marked for this purpose, and if no such place is marked - before the sign. The sign with the words "Rogatka uszkodzona" is put up when the barriers are not working: a raised arm does not then mean that the track is clear, because the device simply does not react to a train. That is why you always stop, even when you cannot see or hear anything, and treat the level crossing as unprotected. From the stopped car you look both ways, and you move off only with the permission of an authorised person or after a signal allowing you to go.

Legal basis: § 26 para. 1 and 2 of the Regulation on road signs and signals; Art. 28 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym)