My personal mooring is very well marked, and I don't use other peoples moorings regardless of if they are marked or not.
As it should be with some common sense exceptions. There are places along the Maine coast with "transient" moorings placed by people who like to stop and enjoy anchorages but don't use them as their primary mooring. There is a SHYC (Seal Harbor Yacht Club) mooring in the anchorage at Baker Island. It is labeled SHYC. It is often used by non members. No one really cares. If it is empty, pick it up. If not drop your hook. There are unmarked balls in locations that would not be permanent locations by virtue of their remoteness. We know the moorings. We stop and have lunch. Might even spend the night if no one shows up by 4:00 pm. We also know when we are entering a mooring field that is home port for private moorings. Those are marked and obviously were put there to provide a home for their owner. No one will object to finding a boat safely tied to their mooring if the party using the spot is available and appreciative enough to say, "Thanks", then move if necessary. I have made some friends by extending their stay because I was tied up someplace else. Friendly, responsible, appreciative mariners are welcome. If you insist that you have a right to my mooring because it was empty when you arrived, we may have a disagreement. I haven't met that dope yet. #228 in SH is rated for a 40' boat. It is inspected and the lines have double chafing gear. It is a double bridle. The location is exposed enough to provide a bit of sea motion over night if it is blowing from the south. There are several balls labeled SHYC in the harbor, too that you can use. Just stop at the yacht club, tell them you were my guest and pay the $20.00 (I think?). There is plenty of depth at the dock to pull along side.
Come down and visit. There are much better places to spend the night than in Seal Harbor. I almost never sleep aboard at my mooring but move to a nearby anchorage if I want a "night out".