Each that card is a physical tangible advertising of some e-book. E-book ad card contains QR code and the annotation of the e-book.
You can take the card with you for free, to give to someone, or just download e-book by QR-code.
Idea offers different audience's involvement levels.
Stand with such cards can be placed on Fairs as well as in bookstores. This is the easiest and cheapest way to make e-book tangible