HVV Switch privatize parking space

Moin. Brief explanation about HVV Switch. This is an association of several Car Sharing Parts in Hamburg which are all united under one app. Now to my question. Here directly in front of my front door were made of public parking spaces, which are made for Switch. Here stands a sign that it is about Switch parking spaces and one gets a contractual penalty of 20 euros per day and can also be towed away. But what interests me a sign which does not occur in the StVO. To privatize direct parking bays on a public street? Lg Tobias