It is the middle sign (its official symbol is F-13) that can be seen in this photo: https://radioszczecin.pl/serwis_informacyjny/pliki/2023/458167/2023-07-05_168854973119.jpg

The general meaning of this sign is quite complicated, as it has many variants (e.g., the indicated route may be recommended or mandatory). All possible applications are described in Polish in sections 7.2.12. and 7.2.13. of this regulation: https://isap.sejm.gov.pl/isap.nsf/download.xsp/WDU20190002311/O/D20192311-c1.pdf - If necessary, I can translate this fragment.

In this case, it signifies a mandatory transit road (a section of detour road) for heavy goods vehicles with a gross vehicle weight of more than 10 t travelling to the town of Gryfino.