One piece of evidence that a society has social divisions would be differences in burial. From the pharoahs to the chieftains of Mississippian polities, political leaders and elites were often buried with accoutrements of power that indicated their position in society.
Archaeologists can also analyze the bones they find, which can often tell them much about diet and wear and tear. These can also be evidence of social stratification, as elites were often better fed, and performed less physical labor than common people.
Evidence of organized religion and complex government, including complex iconographical systems and totems, also often point to social divisions in a society, as they usually accompanied the development of priestly classes as well as the rise of bureaucracies.
Elite vs. non-elite social divisions may be indicated by the presence or absence of mortuary goods and elaborate vs. non-elaborate burial chambers. Rulers and elite members of a society are often given special treatment at burial, e.g., the Pharaohs of Ancient Egypt, the Terracotta Army of the First Emperor of China. The burial chambers for these elite individuals—as well as the numbers and kind of graves goods included with the burials—were expensive in terms of material goods and labor which shows the high status of the individual(s) buried. Even in societies without pyramids, and other large or elaborate burial chambers, archaeologists find evidence of differences in prestige when some individuals are buried with more "elaborate" grave goods, e.g., pottery, flint tools, versus other individuals who are buried with fewer grave goods, less elaborate goods, or none at all.
Social divisions are also indicated through architecture. Monumental architecture suggests a ruling elite able to co-opt the labor of many individuals to build the monument, as well as different levels of social organization/divisions of labor required to organize individuals, work, and planning.
Site hierarchy, in terms of site size and architectural complexity, may also indicate social divisions.
Other evidence of social division in societies may be indicated through nutritiona; differences, where elite or more prestigious members receive better portions of, more of, and higher cuts of meat and other food stuffs. Nutritional differences show up in the teeth and bones of individuals and can be used if there is a comparison population.