Foreign tourists mostly but some citizens, too, in and around Miami and on the Interstates at rest areas. It began to spread to locals in owned cars about the time creative enforcement and tag changes made the phenomenon go away. About that time I started keeping a gun in my car.
I’d guess that foreign tourists are relatively over-represented in car rentals, as close to 100% fly in from abroad while citizen tourists drive in at least to some degree - and the foreign tourists lack “situational awareness” (or just plain orientation) as to what parts of town are better avoided...