Depends on the city I guess, but I'm pretty sure privately owned is the norm. Someone owns the building and land including the sidewalk. Most cities and towns have rules regarding the sidewalk that applies to the property owner. These would be rules for things like snow and ice removal, proper maintenance, and even keeping it clean.

Now.. one company may own the building + sidewalk and the businesses inside the building are just leasing space. In that case, they would probably need the building owner to call the towing company, or have some sort of agreement to do so. For instance, the owner may delegate some sidewalk responsibilities to the round-level tenant in the lease. I have a rental property and I delegate snow removal and lawn maintenance to the tenants. (Though legally, if the tenants don't keep up with it, it would ultimately come back on me).