I made up something like this last year for summer school. I'd say, "Give me 5." Kids would have to raise their little paws, give me their 2 eyes, 2 ears, and one closed mouth to show me they were being respectful, good listeners and ready to learn. It was effective at getting their attention.
This is the BEST idea. As a teacher there will be a lot of this. As a student I saw a lot of this myself. I wasn't talking I was singing. Singing, whispering, whatever you were still TALKING. I would definitely use this in a classroom.
Cute idea... good way to get them to learn square roots without them knowing it because they know the numbers under the post its! It is very inexpensive and not at all time consuming to make. The only problem I can think of with this would be the postit notes loosing their ability to stick onto the clock's face.