i would be arguing that the sign is blocked and hard to see (one on the left)...regardless of the sign on the right hand side of the street, it does not give you adequate warning for no left turn, they should have put it before the turn and not "in the intersection" at least that is how i see it...if you have the time and money, i would show up in court and argue it. you have a clean record, if it's an honest mistake, to me it's worth it...no point the city putting signs up that you can't read properly.
Problem is that it's spring and that tree doesn't have any leaves yet, so the sign is clearly visible (as I discovered post factum)..