Encourage your students with small, tangible thank you notes with these "Caught Being Good" tags. These tags contain 7 different common behaviors that teachers like to see in the classroom. Give these out intermittently when you see a student with model behavior, including students who don't always make the right choices. Often, when students are never sure when a reward will be given, they try even HARDER to please their teacher. This makes for an easy reward system for you. So instead of giving a sticker for every little "please" and "thank you" uttered, give out the occasional "Caught Being Good."
Make copies on colored paper. You might want to use all the same colored paper so (for example) the "green strip" you hand out is easily recognizable by on-looking students. They'll know, without you making an announcement that interrupts the flow of learning, "S/he got a Caught Being Good!" On the other hand, the graphics on each strip will make them "collectible." Kids will ask each other, "Did you get the boy with the book yet?"