S.C. Code § 56-9-358
The security required under this article shall be in the form and in the amount that the Department of Motor Vehicles may require but in no case in excess of the limits specified in Section 56-9-353 in reference to the acceptable limits of a policy or bond. The person depositing security shall specify in writing the person on whose behalf the deposit is made and, at any time while the deposit is in the custody of the Department or State Treasurer, the person depositing it may, in writing, amend the specifications of the persons on whose behalf the deposit is made to include additional persons; but a single deposit of security shall be applicable only on behalf of persons required to furnish security because of the same accident.
S.C. Code § 56-9-358