I live in the SF East Bay. There is a craft store here; Joanne's; they have those kinds of carts where you pay $0.25 to use but you do get it back at check out. They do this so they don't get stolen. Sadly, many homeless use them as their moving home. There are a few grocery stores that do this as well.
In France you have to use a coin to get a cart, only these exists. The brand of these carts is usually Caddie (and that's how we call these carts, it's a normal noun now) so I guess it's specific to that cart brand?
In benefit for those who don't know the system.
Pushing in a coin releases the lock, reconnecting them together liberates the coin.