I've been camping a time or two in my lifetime and I've spoken English all my life.  So when I arrived about 4:50pm at the campground and nobody was in the campsite entrance shack but this sign was posted, I felt I understood what I was supposed to do. The website for the campground indicated that spots were not pre-assigned, so this was not a big surprise.. So, anyhow,  here's what I did:

I drove around the two available loops of camping areas looking at the empty campsites.  After seeing them all, we chose the empty campsite #4.  Backed the trailer into it, leveled it up, put the jacks down - you know, the regular routine.  It took us a couple of tries to get level and in all it was about an hour of fiddling around before we were happy with the settup and all settled in.  At that point we were hungry so I grilled up some hot dogs and we ate dinner.

After dinner, I thought I'd introduce myself to the camphost in spot #21.  I walked over there, brought the printout I had of my online reservation and knocked on his trailer door.  I  introduced myself and told the host we were in spot #4.  He proceeded to tell me that someone was already in spot #4. 

I informed him that it was completely empty with no sign of anyone there or any type of "occupied" notation on it. 

He proceeded to argue that they were camping in a van and perhaps they "went out to dinner".

I told him that I'd been to many campgrounds and that it is customary to leave some sign of occupancy. A small placard that says "occupied", a cooler, heck just a tarp on the table.. anything.

He said "we don't do that in this campground".

Now, instead of discussing the finer points of his debating style or the flaws in the policies of the campground (or perhaps the host) I asked him "well, do I have to move?"

He explained to me, in his non-committal way, that "if they return and ask for the site back, you'll have to move".

I gave a half-hearted "uhh.. ok" and proceeded back to my campsite.  My wife was half-worried that the previous occupants might be in town throwing back a few and when they came back we'd get some drunken pounding on our door at midnight and we'd have to deal with some unpleasantness.

Fortunately the van campers never returned. (I figure they moved to a spot in the other loop and just didn't tell mr. personality about it).