I fought it via mail. It took multiple round trips. At each step the potential fine more than doubled. If I did not respond correctly or in time, I waved my right to appeal. The appeal paperwork contradicted itself. (Page 1: You must do X or we will reject your appeal. Page 2: You must not do X or we will reject your appeal). I had to send a passport photo less than 30 days old of myself in, but photos taken with electronic cameras are not allowed.
In the end, I sent a letter. The city of San Francisco is not obligated to inform me of a successful appeal, so either I beat the ticket, or some day (maybe years from now) they will issue a warrant for my arrest.
This isn't even guilty until proven innocent. 100% of the evidence presented against me proved my innocence, and I will be in legal limbo forever.
[edit: In a special kafka-esque twist, the only reason I was able to fill out the paperwork successfully is because the telephone operator at the SF courthouse took pity on me. There is a number to call for clarification, but no one picks up that phone. So, your best bet is to get your legal advice from the operator.]