You do indeed need a yearly vignette to drive on Swiss motorways.
It costs CHF 40 and needs to be affixed to the windshield to be valid
(in principle, merely having one somewhere in the car isn't enough to avoid a fine).
The vignette for a given year is valid from the beginning of December in the year before until the end of January in the year after.
I don't know for sure
but I doubt you can buy that vignette from car hire companies as far out as Frankfurt and I would be really surprised if you could rely on a rental having one already (as others have suggested you can always ask or be lucky,
but it's not standard).
But you don't need to worry about first entering Switzerland and trying to track down a place that sells it, getting one on the way
is really easy.
Usually, you can buy the Swiss vignette at the last couple of petrol stations/rest areas in Germany (possibly losing one or two euros on the exchange rate but nothing to worry about if it feels more convenient) and at the border itself, certainly on the motorway (smaller border crossings do not have any customs office/staff nowadays but major crossings still do).
travel.stackexchange.com/users/6669/Relaxed
In Germany there are no special vignettes - it's all free.
But yes, as already written in the comments, in Switzerland you need a vignette.
The vignette costs 40 Swiss Francs and will be valid for one year.
There is only this one version.
The vignette is only needed for motorways, not for the rest.
You can buy them at gas stations, or - most often - somewhere at the border.
If you enter Switzerland, watch for some "Vignettes here" signs, or just go to the next gas station.
The vignette has to be put onto the front windshield .
If you just have it, but it is not stuck to the windshield, it is not valid.
travel.stackexchange.com/users/44491/Reto Stauffer
Everthing is clearly explained in the Swiss Autobahnen site .
The vignette is required for most major highways, and costs 40 swiss francs.
In can be bought at "post offices, petrol stations, garages, touring club offices (TCS) and Customs".
The time I used it I had rented a car in Frankfurt.
As far as I recall, I got it at the border.
travel.stackexchange.com/users/10087/Martin Argerami
Edited 1: check with your car rental company about the vignette.
Border areas will most likely provide a car with the vignette already affixed if they know you will be traversing Switzerland.
2
: Renting a vignette is not possible.
Buying one is simple Previously
In Switzerland you need a vignette to use the motorways.
It costs 40 CHF and is available in numerous places.
If you are driving into Switzerland, stop off at the customs and you can buy one there.
Check the Swiss tourist website for more information.
travel.stackexchange.com/users/39399/Reuben Mallaby
Other answers have covered the options of buying a Swiss vignette, however there's one more option you can try.
When you get to the rental agency, ask if they have a car with a Swiss vignette in their inventory.
While this may seem far-fetched, I've actually seen rental cars in Czech Republic with a valid Swiss vignette.
Since they're valid for 14 months and no short-term options exist, any car that's driven into Switzerland in the past year would likely have one stuck on the windshield.
travel.stackexchange.com/users/9009/JonathanReez
Buying a Swiss Vignette is actually very simple and it may be possible to obtain a rental car with Vignette already but usually that will only happen if someone had purchased one when driving to Switzerland.
Having said that to obtain a Vignette all one needs to do is purchase one at the border from the police officer.
Lanes while crossing the border are divided into 2 lanes left for the through traffic and right for the local or traffic that needs vignettes or have other business at the border.
Driving to the right
you will be greeted by a police office who will happily sell you a Vignette for 40CHF or 40 Euro.
travel.stackexchange.com/users/1372/Karlson
When I last travelled to switzerland by car
I was able to buy a Vignette in Frankfurt, at ADAC
travel.stackexchange.com/users/44513/Anatol
To drive on Swiss motorways if I recall correctly one needs a  Vignette  based on what I have been reading I should be able to buy it at  various places  in the country.  I am renting a car in Frankfurt and my travels will take me through Switzerland for a day or 2 so it begs the question:   Do car rental companies in Germany provide a Vignette for the car already?   or   Can I buy or rent a Swiss Vignette from them?
Do you need a Vignette to travel the roads of Switzerland, and how can I obtain one?
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<germany><car-rentals><automobiles><switzerland>
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travel.stackexchange.com/users/1372/Karlson
You do need a Vignette to travel on Swiss motorways, but not other roads. Vignettes are valid for a year and are available at post offices, petrol stations, garages, touring club offices (TCS) and Customs, but you may be able to rent a car that already has a Vignette on the windshield. A vignette is required for driving on motorways in Switzerland. They can be purchased at the border, in gas stations and at post offices. The cost is 40 francs and they must be placed in the windscreen.
A vignette is required for driving on motorways in Switzerland. A vignette can be bought at the border, in gas stations, at post offices and the rental company may have cars that already have the vignetted. The vignette costs 40 francs and must be placed in the windscreen.