S.C. Code § 7-15-210
The return-addressed envelope required by item (4) of Section 7-15-200 to be sent to each absentee ballot applicant shall have printed on its face in the upper left hand corner the words "Absentee ballots for __________ County, __________ (county seat), South Carolina." All blanks on the face of the envelope shall be filled in by the board of voter registration and elections prior to the mailing of the ballot to the absentee ballot applicant. On the back shall appear blanks which the voter shall fill in with his name and address. The envelope shall be of such thickness as to make it impossible to read any of its contents without opening the envelope. When the ballot is for use in a primary election the return-addressed envelope referred to herein and in Section 7-15-200 shall be changed appropriately to insure its return to the proper county committee.
S.C. Code § 7-15-210