If you get a jobsworth cop then they will give you a 20 chf fine for not having the original. I never have the original in the car. There have been many cases of people simply re registering the car in their name when going for test drives .. A famous one was a rental car case.
This user would like to thank rob1 for this useful post:
Get one if those magnetic ones from Jumbo or Migros Do It then you'll just be able to take it off when they get back to Switzerland.
don't have time anymore, they leave tomorrow morning and I bought the self-adhesive one. On the back window I wouldn't mind as I'll just get it off once they are back. But I'd rather not put it on the paint...