I will be buying a new car and selling my old one. Should I remove the old decal and place it on the new car window ?

Yes, remove your old decal. Then contact NTTA of your car change they will provide with new decal.

Yes contact NTTA through your online account explain to them you've sold your car you remove the sticker otherwise the person that buys the car can use the sticker and they will charge you and that a will ask you questions about your new car like your license plate number and all that but be sure and take the old sticker off the windshield of your old car sometimes they may tear if it does go to the online account and let them know that it tore and they will tell you when to come in and get a new sticker

You will have take your new car too the NTTA and let them know that your sold your old car and bought a new car so that you can register the new car and get a new Toll Tag for it.

It is great to remove the old toll tag; you will need to go and exchange it for a new one. It is registered not only in your name, but the vehicle color, make, model and VIN. Please don't forget to bring proof of insurance with you, too. That will have all your new vehicle information on it.

If you don't contact NTTA leave that sticker on there the new person can use it that buys your car until you cancel it.

As long as you contact ntta, before you sell your car, they will cancel that toll tag right then and you can just leave it on the windshield of the old car. It won't register to the new owner. You can also call, send or email if you have a online account with ntta or go there to and pick up your new tag. Etc. The only thing is by mail it can takes about 7-10 days to receive but in person you get same day.