The sticker must be attached to a non-removable part of the trailer, most commonly on the drawbar, a non-removable front panel or metal part.
Important: Once the sticker is attached, do not try to remove it, this will destroy the sticker and a new sticker has to be purchased. Do not use any kind of adhesive or tape, this also leads to the sticker becoming invalid. Same penalties apply as for driving without a vignette.
Related articles:
Can I remove and reuse a physical Swiss vignette (Sticker)?
Can I get a refund for a destroyed Swiss sticker?
Damaged Swiss sticker vignette
Where has the Swiss sticker to be placed on windshields of cars, campervans and caravans?