Parking in San Francisco is a serious no-holds-barred business. If you manage to get a garage space, selling your car to buy a car that fits is “normal”. I have friends who figured that ‘n’ parking tickets a month was cheaper then the cost of renting a garage, even if they could find one. So, people who do finally manage to have a parking garage space get frustrated by street parking blocking in their driveway. Towing companies make a lot of money around here.
Signs like this are routinely ignored:

…but signs like this are rarely ignored!