I like this idea, it would be original. Plus, it would motivate your students to answer your questions and work more in class, since they would get some "gratification", which would be harmless since there won't be any competition between students.
How old are your students?
When I was in school, there was a similar system which consisted in "images" (french word). When you worked well in class or when you were involved in class, you would get an image, which was a little drawing on paper with a title (and maybe a number but I'm not sure). You could collect them by answering well to the teacher's questions in class, and then show them proudly to your family and friends. It was a nice system but I don't think it exists anymore.