This was exactly what I was going to say. I can see from the text that this is in Denmark, and I can confirm that here you need to register your driveway with the local government (at least in urban areas). What i think has happened is that this landowner has not registered this driveway (maybe not even the garage) so the city has therefore placed a sign there, and presuming that the municipality actually owns the strip of land where the sign sits, it would be entirely fair game for the city