During our recent trip to Florence, a notoriously car-unfriendly city, I found this car park. I forgot to take a picture, but it obviously once was a paid car park that has been abandoned since. (By the authorities that is, not so much by the drivers.) The small building at the northern end looks like it might have served for the personnel and at the entrance and exit there are what looks like remains of lift gates that have been broken or sawn off. There are no blue signs with white "P" on them but there are no parking restrictions either. Many of the cars there were covered with a thick layer of dust, some had long (as in months) overdue parking tickets behind their wipers, others looked quite ordinary and came and went during our stay.
I asked some passers-by and all of them confirmed that it was ok to park there and that the locals regularly do so, only that we shouldn't leave anything of value in the car. I left the car there and it was still there the next day, quite happy and unharmed.
Of course, I mapped the whole thing and proudly added a "fee=no". The trouble is, technically it's not an "amenity=parking" at all because it's not designated as such on-site. "disused:amenity=parking" comes to mind but it's not disused either, as people keep using it. "access=permissive" and possibly "access=discouraged" come close but not quite. So I added "informal=yes" like some footpaths have, although the car park certainly was "intentionally established" and didn't just "evolve", as the Wiki defines it. Actually, I'm pretty sure I know at least a few car parks where "informal=yes" would fit perfectly, but this isn't one of them.
So, do we have a better way of dealing with this?