We've stayed at Walmarts, Home Depots, Staples/Office Max, K-Marts, Strip Malls, Casinos++, outside gates to SP's if arriving too late, and Rest Areas if well lit and typically many have had security patrols we've stayed at and confirmed we are good. In Wyoming we found signs saying No Overnight Camping, but noticed folks were, asked a patrol car that came through and they said it was so they could move on undesirables and to feel free to stay overnight rather than drive tired.
Lake Havasu security guards have moved us on as per Ordinance as soon as stores readying to close, but there is BLM nearby.
Varies by area and city ordinance but don't just take No Overnight at rest areas as gospel = ask rather than go to sleep at the wheel and crash!