S.D. Codified Laws § 32-22-47
The board of county commissioners of any county, the board of supervisors of any township, the board of trustees of any road district, or the Department of Transportation, shall erect and maintain at a point on the right-of-way and within six hundred feet of both entrances to any bridge and may, where it is deemed necessary, erect and maintain at the nearest road intersection in each direction from any bridge, upon any public highway which it is the duty of the board or department to maintain and repair, a conspicuous sign specifying in large numerals, the maximum weight of any vehicle, laden or unladen, which may enter upon or cross over the bridge. No bridge signing is necessary for bridges which can accommodate motor vehicles operating under the legal weight maximums provided in § 32-22-16.
SDCL 32-22-47