A little while back, the San Francisco MTA issued me a parking ticket because my wheels were "insufficiently" turned to the curb. In actuality, my wheels were touching the curb, which meets the requirement that the curb act as a "check" to a potential runaway vehicle on any street with a slope exceeding three degrees.
I asked an MTA enforcement agent the next day (I'm pretty sure it was the guy who issued the ticket) whether it could be appealed and he basically replied, "You won't win, because you can't prove the enforcement agent made a mistake." He further explained that the MTA has a "performance requirement" which compels agents to issue tickets for sidewalk parking and wheel infractions so that lazy enforcement agents don't simply follow the street-cleaners and issue tickets for street-cleaning violations.
As I thanked him for his time, I couldn't help but notice the front wheel on his unattended vehicle.