msdn link

The SAMPR_SID_INFORMATION structure holds a SID pointer.

 typedef struct _SAMPR_SID_INFORMATION {
      PRPC_SID SidPointer;
    } SAMPR_SID_INFORMATION,
     *PSAMPR_SID_INFORMATION;

SidPointer:  A pointer to a SID value, as described in [MS-DTYP] section 2.4.2.3.