Certain countries require vehicles traveling on motorways and autobahns to display a special windshield or windscreen sticker known as a "vignette." These can be purchased at car rental offices,  border crossings,  gas stations... and prices will vary depending  on the duration.

Countries that require "vignettes" are: Austria, Bulgaria, Czech Republic, Hungary, Romania, Slovakia, Slovenia and Switzerland.

You can find travel advise and information for different countries on:
https://www.gov.uk/foreign-travel-advice