I use these in my elementary classroom as a simple visual to remind students of appropriate voice levels. I cut and laminate each card, then clip the proper one onto the board during an activity.
0 - No Talking
2 - Table Talk
3 - Strong Speaker
4 - Outside
I also use hand signals to show on a scale of 0-4 where the noise should be. The combination of visuals and hand signals really helps my students to stay on task!