Go out to the speed limit sign with black spray paint and paint a 4 over the 2 so the sign says the speed limit is 40. Take a camera and set the date and time to right after you received the ticket, and then take a photo of the speed limit sign with a time stamp on the photo. Take it to court and say that you couldn't possibly have known you were speeding because some bad person vandalized the speed limit signs.
Just don't get caught. You will wish you had paid the money if you do.