I didn't downvote you by the way, was someone else. I am in holiday in Spain and surrounded by the use of the word Libre regarding libraries and books. So the same thought as your own also crossed my mind.
That's not really "libre", but either libro (book) or librería (bookshop).
You may see libre on parkings [0].
[0] https://www.burguet.es/fotos/cartel_vinilo_retroiluminado.jp...