What does the © Cartronics mean?

It means that Cartronics maintains a copyright on each of the screens where it appears. While you are free to download and save a copy of any of the screens, you may not reproduce any of these copyrighted screens on your own computer or for distribution to any other person. You may not modify, publish, transmit, create derivative works or in any way exploit any of the copyrighted material. To do so, except as otherwise provided above, violates the copyright laws and is subject to potential civil and criminal penalties.
Any rights not expressly granted herein are reserved by Cartronics.