Differential Settlement can show up in vertical cracks along walls as well as horizontal cracks in floors. However not all cracking in the slab on grade indicates differential settlement. Some other reasons you may find cracking in the slab are; Concrete shrinkage and curing, stress and poor construction.
Here is a site that shows different types of cracks and what they indicate. “Causes of Basement Floor Cracks and What to Do About Them | News and Events for Basement Systems, Inc.”