How can I remove highway vignettes and other miscellaneous stickers from the windshield of my car?

@choster already covered all the details but a simpler answer is: Just do it, it's really easy (much easier, in my experience, than removing price tags or the type of stickers described in the other question). There is really no need to be too smart about it.

A razor blade as scrapper makes it slightly easier but in my experience removing a vignette after one year is not a problem at all (removing it earlier might be, I don't know). It's true that the vignette is typically designed to fall apart when removed but that's OK. There might be some minute traces of adhesive left on the windshield as well but it never bothered me either. You can just put the next vignette on the same spot.

The main reason people worry so much about solvents, scrappers and other tricks is to avoid damaging the vignette (which is only important if you want to cheat and transfer it to another car). I don't do this but a friend of mine once used hand cream (applied directly to the windshield before the sticker) to make it easier to remove the vignette and it worked fine.

This answer is based on my personal experience with the Swiss (virtually every year for decades) and Austrian (a few times) motorway vignettes, I don't have any first-hand experience with other countries.

There are two types of situations, in my opinion:

1. You have to stick the vignette yourself;
2. Someone else has done it, and now you have to undo it, without leaving adhesive marks on the windshield, where they can be naggingly obvious.

As I travel a lot through Europe and these things are still mandatory in some countries, and I only need one for 10 days or so, what I usually do is stick the vignette once or twice heartily to my jeans. An then stick it to the windshield. Apparently the lint and micro fibers from clothes adhere to the vignette and decrease its grip while being an invisible free solution.

If someone else has stuck the thing to the windshield, the deed is done. Quickest way is scraper and alcohol, as I do not recommend WD40 or lighter fluid simply because they are inflammable and highly volatile. In other words, dangerous in the confined space of a vehicle. And also, they smell pretty bad.

You can also try using a hairdryer to heat up the sticker, after which it will peel off the windshield with little to no residue left behind. It doesn't need to get too hot; 30 seconds should be more than enough if the ambient air temperature is 20C. The hairdryer works for me when removing UPC stickers off of boxes for mail-in rebates.

You need a product called Sticker Shield. Basically it is a piece of transparent plastic that the sticker sticks to, then the plastic sticks to your window. Reportedly the stickers look just like permanently attached stickers.

(I bet if you could find the right plastic you could just make your own too. It's like the phone screen protector idea but these things are removable, designed so you can swap a "permanent" parking pass or similar between multiple vehicles.)

This comes from Cool Tools, A Catalog of Possibilities, by Kevin Kelly, the submission by Joseph Stirt. I can't recommend this book highly enough. Anyone who sees mine wants it.

Please excuse the overly commercial-looking links. I can't find much of a web page for the product, just the order form. I have no connection with the Sticker Shield people or Cool Tools.