Sorting a book pile into bands is a lovely afternoon; keeping it sorted needs labels. Pick your bands, say how many of each, print a sheet (21 labels per A4), and stick them on covers or storage boxes. Works for home libraries, class book corners, and the crate of hand-me-downs nobody's dared sort. No signup, nothing uploaded.
Print in colour on paper + sticky tape or glue, or straight onto sticker paper (A4 label sheets, 21-per-sheet layout works well). Bands and level numbers follow the standard UK book-band ladder — the same one our Phonics Book Finder uses. Enable "background graphics" in your print dialog so the colours print.