Austria requires Toll stickers on all vehicles travelling on their motorways and highways. You can purchase these stickers from post offices and petrol stations or the Austrian Automobile Clubs. Neighbouring countries also sell these stickers. If you fail to provide this sticker, you will be fined.
Streetcard ALWAYS have it...you don´t! And another interesting tidbit...apparently, if you stop at an intersection where you have the right of way (because you´re looking for a sign or a number or just didn´t know...) you lose your right of way! Can cause some major differences of opinion in traffic!