i agree with taking a picture of the sign, at night and during the day and show the judge where the cop was parked

and as for you exhaust, tell him to give you the stock decible reading of a 96 200SX SE-R, and then with a calibrated decible-meter to go and test your car, and if they can prove it beyond a reasonable shadow of a doubt, then pay it, if not, screw them

the law says you can't have an exhaust louder than stock, not modified, but louder, so tell them to prove it, and if they say just listen to it, say hey, it doesn't sound louder to me, your perceiving it louder...so shutup

good luck man