This assignment comes from the Complete Book of Speech Communication by Carol Marrs (who was my junior high speech teacher and influenced me to become a speech teacher.)  I use it during the listening portion in my communication applications classes.  I tell my students that since they can't talk, they might as well work on their listening skills.  Most students hate it, but some actually get into it.  I do grade them on it despite the fact that I know they cheat.  To get a 100 they have to be successful in every class (the teacher signs the form) and at home (parents sign).  I also have them write about their assignment after the 24 hours is up.  I usually start it about the last five minutes of whatever class they are in and they don't get to talk again until the last five minutes of class the next day.  (Obviously, you shouldn't do this on a Friday.) 

I print the badges on colored paper, cut them apart and laminate them to give to the students.  They have to wear them while they are participating.