I think that a site needs to be both paid for and occupied in order to belong to someone. But how can you tell? I have a small class C, no toad. If I arrive, pay, put the tag in my RV windshield as directed, leave a camp chair in the driveway, and go off somewhere for sightseeing, the site might not look either paid or occupied to someone else.
BTW, my camp chair has a sign: "Site occupied" and my RV's license plate number. Maybe I should add a photo of the RV?
Yes, I know that some places indicate paid status by tag clipped to post. Where I camp maybe half do that and the other half want the tag in the windshield.