It depends on when and where you park and for how long. You obviously don't want to park in handicap spaces or valet spaces without permits, and you won't want to park there overnight.
Obviously, first is to not park in a place you're not supposed to. If you legitimately didn't know, try to show proof by taking pictures of the place you parked in. Show how a sign was obscured by a...
No. We "had" a sign where i used to live and everytime it was replaced at night all the people on my street would go and cut it down with an angle grinder. Then no one could get a ticket.