The Sep 1st thing is exclusively a Boston phenomena. No other cities, as far as I've ever heard, have such a bizarre seasonal operating transition (and I've lived in much bigger college towns that still didnt operate like that).

The rental signs are hit or miss. For example, the Biledou rental signs in Wayland square have been there since I moved here a decade ago. Some get changed out or are temporary, but a lot are permanent fixtures on properties that may or may not have openings.