This year my students have Piano Key Chains that we use for a variety of things; one of which is memorization. My students are encouraged to memorize pieces they are working on. For each piece they can play from memory (with all the dynamics and articulations in place without prompting from me) they get a hole punched in their "Memorization Card" on the key chain.
Claire has already received 2 holes in her card for memorizing pieces. For each piece, my students receive a reward of 3 bonus beads on their practice chains.