While I agree with flyingron in general, it is possible to convince a court or prosecutor to dismiss a ticket based upon the fact that a sign is obscured. He's also correct that it's not a "gimme". When you're attempting to prove that a sign was obscured, you should anticipate that the court or prosecutor will want to see a picture that clarifies how visible the sign is when you're actually stopped behind the stop sign, as well as a distance shot showing that you did not also overlook a other signs or pavement markings.

