The white notice says the following "This is a unique and well used facility but to operate efficiently, an exchange of books is essential. If you take a book, please leave one in its place for the continuing success of the book exchange and the enjoyment of all its users. Thank You."
It reminds me of tourist fales in Samoa and backpackers in different parts of the world where there is a bookshelf for travellers to leave a book they finish reading and swap it for one left by a previous traveller. If e-readers take over there won't be a need to exchange bag and beach battered books. That would be a shame because it's interesting to see what other travellers have been reading.
Image by David Hillas