"If you're California you regulate stuff. It's what you do"
<insert car insurance sales pitch here>
Why couldn't the city couldn't just impound and auction scooters, bikes, skateboards, shopping carts that are parked illegally? They almost certainly can do this under one of the bajillion existing statutes. Don't want you crap stolen by the government, don't let your users park it in dumb places. As I understand it riding a scooter on the sidewalk is already illegal. I don't see how this is any different from bike sharing other than the form factor making them more tempting to ride on the sidewalk.