This is a great idea, better than a strip of paper pinned or a piece of tape stuck to fabric with the number or letter on it. My kids always manage to think the tape is a mistake and try to "clean" it up. I never have piece or row markers in the same place they started they normally end up in the trash! I'll have to invest in some number beads!
I think I have some polymer clay might put the same kids to work making some. lol