The recessed design is a favored effect for the front cover of a book. There are a lot of people that want the front cover decorated with some sign or symbol that would identify themselves as the author / owner or describe the contents of the book.
The example to the right is the symbol for the planet earth from the Stargate television series/ movie. Designs such as this (fairly simple shapes) are easily added to the cover of a book and the cover material (often paper or leather) is pressed into the design.
This element can be used to add a symbol, surround the symbol with a border or the like. The recessed design is often cut into the boards about 1/8th of an inch deep but can me made further depending on the materials involved.