Here it is:
Sticker Shield
They work great; easy on; easy off; supposedly restickable to some degree (although I just leave them on for a year at a time, they are always still sticky when I do that)
They peel right off when you don't need it anymore. I have never tried them on vinyl, but they are considerably less sticky than the permit stickers themselves, so I imagine it would come off just as easily. For a few bucks, it's worth a test -- they come 2 to a pack.