S.D. Codified Laws § 32-17-22
Any vehicle, operated by a person authorized to carry United States mail, may be equipped with a single rotating beacon light or lamps to warn the operators of other vehicles of the presence of a vehicular traffic hazard requiring the exercise of unusual care in approaching, overtaking, or passing. Such equipped vehicle may display such warning in addition to any other warning signals required by this chapter. The beacon or lamps herein provided shall be used only while such vehicle is actually carrying United States mail. The beacon light shall be visible three hundred sixty degrees and be a white or amber light, or any shade of color between white and amber. The lamps used to display such warning to the front shall be mounted at the same level and as widely spaced laterally as practicable, and shall display simultaneously flashing white or amber lights, or any shade of color between white and amber. The lamps used to display such warning to the rear shall be mounted at the same level and as widely spaced laterally as practicable and shall show simultaneously flashing white or amber lights, or any shade of color between white and amber. These warning lights shall be visible from a distance of not less than five hundred feet under normal atmospheric conditions at night. A violation of this section is a petty offense.
SDCL 32-17-22