Originally Posted by KLouis

That is a public (i.e. municipal) parking lot; unless you get there very early in the morning, the chance of finding a spot is rather small. Moreover, this is a "blue zone", which means that you have a limited time of free parking that is certainly not enough to visit Pompei (60 minutes?). Given the fact that it is next to the police station, a ticket is almost unavoidable.

Unrelated to Pompei: I remember back in '89: I parked, overnight, right in front of the police station at Baccoli (other end of the Naples bay. When I went to pick the car the next day, it had been opened and a (cheap) straw hat was missing! Talking about thieves' fearing the police.