Neil, I do not see where "Bill" ever asked for proof. He is just ignoring the registered letter, hoping it will go away. Did he ask for proof or a photo of the license plate? He doesn't say, so one may assume he did not. Or if he did, he is deliberately ignoring the response.
I think this is a good example of an "attitude" that gives American tourists a bad reputation. Neither of you shows the slightest respect for Swiss law. To you, if there are no consequences in terms of a bad credit report or an arrest, it doesn't matter and you need not respect the citation.
As for Bill not recognizing the place named on the ticket, I thought I explained that. Switzerland has a lot of small place names. If you take a local train between two points your train will stop at countless places you never heard of, and whose existence you would never have known had you not printed out the train schedule so you would know where to get off the train. If you are driving between two destinations, you will pass countless places with names you will never know. It may be the name of a crossroad, or a farm, or a church, or other significant landmark.
Did he ever try to confirm the name of the place with Google or a map? I bet not.
The Swiss authorities are, in my experience from many trips there, extremely reliable, precise, and honest.
I hope Bill will keep us posted on his further adventures when he returns to Europe and rent a car.
John, I hope it is clear from this discussion that you should pay the fine. Or contest it if you like, and ask for proof. But at least respond; don't just ignore it.