SDCL § 31-28-10: Marking intrastate and interstate highways--Uniformity--Conformity with other states.

The department may classify, designate, and mark both intrastate and interstate highways lying within the boundaries of this state and provide a uniform system of marking and signing the highways under the jurisdiction of this state. The system of marking and signing shall correlate with and so far as possible conform to the system adopted in other states.