This is a template for a "STOP" sign that I use in my classroom. I found this idea on Pinterest a few years ago that other teachers have blogged, and we have all found it very effective. I have a set printed and laminated, and I implement them as a non-verbal behaviour management tool in my class. To avoid disruption to my lesson, if students are doing the wrong thing I simply place one of these on their desk as a warning, and they know to redirect their attention to the lesson.
Give it a go - your voice will thank you for it at the end of the day.