This is the display I leave up all year long. I use a chalkboard with laminated music notes with magnets on the back of each one. I love these adhesive magnet rolls! They are so useful for sticking on the back of visual aids so they stick to the board.
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!" ;-)
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!" ;-)
