This is something I am trying out this year as a formative check for turning in assignments. Students will have four turn-in trays, each labeled with a different emoji picture. Each emoji demonstrates a rating for how they feel they are understanding the topic or lesson. They will put the assignment in whichever tray corresponds with their feeling about the assignment. This a great way to do quick checks for understanding and also teaches students to self-assess their work.
Included is a "Turn in" sign to hang, four emoji faces, and another sign to hang that explains what each emoji means as far as understanding.