I would take a picture of the location where you parked and dispute it. I know someone who easily got a ticket dropped because they had supposedly parked in a "painted" loading zone. There was a sign, but the "zone" supposedly covered a good chunk of curb that was painted yellow. Except the yellow paint had been long worn off and the person was a good ways away from the sign. She got the ticket dropped and the city actually came out within just a few weeks to repaint.