At the same time, if that sign pops up four weeks in a row and is taken down four times - I should hope the city allocates a bit of labour to actually figure out who is doing it.

And that's the answer that GR doesn't want to hear - clear patterns of abuse are apparent and they need to allocate more manual labour into moderation - automatic moderation can get pretty decent accuracy, but there's always a grey zone where you need some manual review - as much as we shrink that zone I don't think we'll ever make it disappear.