Book Tongue is a printed cloth label, similar to that found on the back of underwear or in fact most modern garments.

For all books it would be attached directly to the spine at the binding stage. Hardbacks would need a small slot cut in the printed cover to allow it to poke through.

Instead of the washing instructions on items of clothing, it has the printed title of the tome, but its primary function is to enable you to pull the book out from between the clamping action of other adjacent volumes gripping it laterally on a crowded shelf.
-- xenzag, Dec 30 2007

Some leather-bound hardbacks have a ribbon included as a bookmark that can serve that purpose. The only ones I can think of are green and red, with horzontal gold strips on the spine. I think they were Readers' Digest books.
-- marklar, Dec 30 2007



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