I have tried several of these ideas and, for some reason, don't stick to one. They all do work.
I was watching a YouTube video by Jordan Fabrics this morning and she used the peel off clear address labels. She wrote on them first and then peeled them off and put them on her blocks. I tried painter's tape once but would sometimes iron over it and got a big mess! So I am not sure if the labels would work for me.
I might give it a try though.