Totally agree with reading the signs but still some of it is not complete. Last night while parking in downtown, there were no signs that ready (after 6 it's free) or anything like that, if I didn't know about that then I would've paid.
On another parking spot around North Beach, parked on one of those 2 hours only unmetered parking (MON-SAT 8 am to 9 pm) for 4 hours (4 pm to 8 pm), no ticket no nothing.