You could certainly fight the charge. However, most days, the police have cameras in their vehicles. If you did in fact perform an illegal turn and they have it on tape, don't tell the judge you didn't commit the act. If it's not on video, then you might be able to tell the judge that you didn't do it. But, it's better to be innocent than guilty.
If you did not see the sign, you could possibly argue that in court. For example and in some cases, if a sign is impaired by another object, then you can't be legally charged unless you know for a fact what the sign says. If the sign is impaired by a tree, bush, etc, how would you know what it said? You wouldn't and only the police would because they are sure to be familiar with the signs in the area.
If the police have the proof on video, your chances to argue falsely being charged, will fail. If no proof is provided by the police and you have a valid reason why you did the illegal turn, then by all means argue it. You also have to weigh out the difference between the time you spend in court and what the actual cost is to the crime. In some cases, you can argue a $100 ticket, but if the judge decides you were in the wrong and you argue you weren't, the judge could actually impose the maximum charge, which could be higher than what the police charged. Be careful and weigh the odds. Most importantly, be very respectful of the judge and police if you do go to court.
