This is using the Gestalt principle where we are using positive and negative space. The negative space of the coffee cup is actually a person talking and the top of the coffee cup comes out to be a thought bubble.
This simple motivational poster uses the negative space inside the "D" and the "O" to incorporate more letters to create a straight forward message. This is a great example of how negative space can be effectively used to bolster a design's message.
06 Semester Test Project: Geometric/Low Poly Design