Disclaimer: This is really silly and you probably shouldn't do it but it's fun to know what's possible.
Did you know you can grade with emoji in Canvas? It's true!
All you have to do is create a grading scheme like you normally would (How do I add a grading scheme in a course?) but instead of assigning letters, you assign emoji!* You don't have to do this course wide since you can use different grading schemes on individual assignments (How do I add a grading scheme to an Assignment?)
Here's an example Grading Scheme I setup to show how it works:
Here's how it looks in the Gradebook to a Teacher:
And finally here's how it looks in the Student view:
I tested this on OSX, iOS, and Android and it worked as expected. Emoji support varies from device to device since it's up to the device to render the emoji, not Canvas. If you are going to do this make sure to use emoji that are likely to be supported on every device, and not just new or obscure ones.
* Not sure how to get to the emoji keyboard? Go read the guide for your OS: