Google’s Satyajeet Salgar announced on Twitter that Google has brought their “book preview” feature which you have seen on Google desktop search, now on the mobile search results. So if you belong to a region where book previews are available, e.g., United States, and previews are available for a book within Google Book search, Google will show you the “preview book” icon.
Below is the screenshot:
Satyajeet said “From now onwards, you can preview books on Google on your mobile.”
When you click on the icon of the preview book, it will take you into a mobile friendly view of the book preview interface in Google Book Search.