We like to use emojis instead of grades because it helps students focus on the feedback instead of a number.
You can put emojis in the grade input using your computer (it's not a built in app feature yet).
On a Windows device you can use the shortcut Windows + ;
On a Mac you can use the shortcut Command + Control + Spacebar.
Just be aware that the emojis don't always look the same between devices, so it's good to test out a few with your students before using them extensively. I use the checkmark ✓, thumbs up, and fire emojis a lot.