You were cited for violating New York City Traffic Rules 4-06 (a1) - speeding in an unposted zone.
Since the officer clearly stated that the speed limit sign was obscured, you can't be held responsible for that posted limit, thus the unposted limit is in effect. THAT limit is 30 mph.
It doesn't matter what the posted speed was because it didn't apply here. My guess was that it was 30 or maybe 35 if it was on the street.
Go ahead and appeal (it'll cost you) but you don't stand much of a chance.