There is one eighth note cut out for each classroom. At the beginning of each lesson, I put up these letters on the chalkboard (with magnets on the back, of course).
When the class is noisy, I remove a letter. When the class is quiet, I add a letter. At the end of each lesson, if there is at least one letter left on the board, the class music note gets moved over one measure. (I ask a well-behaved student to move the note over, and I give him/her a music award.) I find that moving a note up can be more effective to encourage good behavior than moving notes down.
For this reason, I also have a set of gold letters. I add one letter at a time to reward them if they haven’t lost their other letters. I am very stingy with these letters. If they receive any gold letters, they can move their music note over a total of 2 spaces. When they ask me, “What do we get if we earn ALL of the gold letters?” And I tell them, “It’s never happened, so I don’t know!”