Does this sign permit only electric vehicles to enter the green transport zone?

In the picture there is sign D-54 "green transport zone" (strefa czystego transportu): a white rectangle with the word "Strefa" (zone) and a green circle with a car symbol. The sign does not allow only electric vehicles to enter the zone. The answer is: no.

The Regulation on road signs and signals states that sign D-54 marks the entry to a green transport zone. Who may enter it is decided by the Act on Electromobility and Alternative Fuels and the resolution of the municipal council: under the Act, electric vehicles and vehicles powered by hydrogen and natural gas may enter, as well as vehicles exempt from the restrictions, for example those of the Police, the fire service, the rescue services and persons with disabilities; the municipal council may additionally allow combustion-engine vehicles that meet specific conditions, usually a Euro emission standard or a year of manufacture. So the zone is not reserved only for electric cars - in practice, Polish zones allow most newer petrol and diesel cars. Depending on the resolution, vehicles that are allowed in are marked with a sticker on the windscreen or checked by their registration number in the register. Before entering, you check the rules of the specific zone on the city's website, because they may differ; the law provides for a fine for entering without permission.

Legal basis: § 60d of the Regulation on road signs and signals; Art. 39 of the Act on Electromobility and Alternative Fuels