Over here, if your lights were obscured and you had no other way of carrying the bikes without obscuring the lights, the cop might not have just cited you, he might have put a big red sticker on your windscreen that would have made the vehicle illegal to drive - even to drive it home, until it was subject to a satisfactory inspection. You would've had to have the car towed and arranged alternative transport for yourselves, then removed the rack and had the car towed to an inspection center to have the red sticker removed. I confess, I have only heard of this happening once, to a driver who really wound the officer up when he could have gotten away with a warning - absurd, but well within the road safety laws.

As to registration plates; in this state, you're required to purchase a small duplicate plate made specifically for mounting on bike racks, and you can be fined for not having one. That said, no-one I know has ever had one and I've heard of no fines .