Last time I was in Switzerland I wondered if I couldn't just tape the vignette to the windshield and take it with me (for resale on eBay, for instance) after the trip. But I believe I read on the back of the sticker that it was required to stick it directly onto the windshield. And it's designed to look different, perhaps even from the distance of a passing police car, if it's not adhered directly to the windshield.

But I wonder, if I were pulled over and found to actually have the sticker, but have it taped to the windshield and not adhered directly to it, whether the penalty would be significantly less than not having the sticker at all (and therefore perhaps worth the risk).