Terms of Use wrote:

5.4 The Scratch name, Scratch logo, Scratch Day logo, Scratch Cat, and Gobo are Trademarks owned by the Scratch Team. The MIT name and logo are Trademarks owned by the Massachusetts Institute of Technology. Unless you are licensed by Scratch under a specific licensing program or agreement, you may not use these logos to label, promote, or endorse any product or service. You may use the Scratch Logo to refer to the Scratch website and programming language.

FAQ wrote:

May I use / remix Scratch support materials, sprites, images, sounds or sample projects I’ve found on the website?
Yes: Most Scratch support materials on the Scratch website are available under the Creative Commons Attribution-ShareAlike license. There are a few exceptions: the Scratch Logo, Scratch Cat, Gobo, Pico, Nano, Giga, and Tera are Scratch trademarks, and can not be used without explicit permission from the Scratch Team.

https://github.com/LLK/scratch-gui/blob/develop/TRADEMARK wrote:

The Scratch trademarks, including the Scratch name, logo, the Scratch Cat, Gobo, Pico, Nano, Tera and Giga graphics (the “Marks”), are property of the Massachusetts Institute of Technology (MIT). Marks may not be used to endorse or promote products derived from this software without specific prior written permission.