contesting a moving violation

Turned onto a highway onramp yesterday (slow moving, fairly heavy traffic) and a motorcycle cop jumps out into the traffic and pulls over 3 of us who made the right turn. Tells us it was illegal and it's a $100 ticket. I look back down the road and the no right turn sign is a good 3 car lengths behind the signal stop line - no sign whatsoever across the street on the signal or anywhere else - no indication anywhere else that you shouldn't make the turn.

Obviously set up to be a trap as lots of people are making the turn and they have two moto cops just camped out pulling people over out of the slow traffic on foot.

Anyone contested one of these before? Any tips? (this is Hawaii btw)

Thanks!