"When the bank which belongs to its customers insures them, that changes everything" says the poster.
I'm not really very sure what it means, but it's just fancy marketing blah-blah in the end, so it doesn't really have any significance I guess.
There is a certain irony, though, to see how the bank (or its doorway in any case) is unwittingly providing a certain kind of assurance to someone who I would think is probably not one of their customers. Indeed, they are practically providing a home, albeit a purely nocturnal one, in a highly sought after central Paris district, free of charge, and when you think how difficult it is to extract money out of them for practically anything these days, this is quite remarkable in itself.
So let's hear it for Crédit Mutuel: you don't even have to be a client and they'll put you up for free all over the city; now that's what I call customer service.