This was one of my favorite practice incentives in my piano studio. Students got to hammer a brass nail into a real log if I determined that they had practiced. Yes, I made the decision. Parents didn't have to keep a record or sign anything. I listened to the students as they played their song of the week. And yes, they practiced songs because beginning piano students exclusively learn how to play the piano using singing games.
Students knew that to earn the privilege of using the hammer and nail, they had to demonstrate by their playing that they had practiced. That didn't mean perfection, just evidence of improvement.
Here's what I did with the practice log. It reminds me of my sweet students every time I see it!