/sys$common/syshlp/helplib.hlb BACKUP Command, Qualifiers, /COMMENT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /COMMENT=string

    Output Save-Set Qualifier

    Places the string that you supply into the BACKUP summary record
    of the output save set. Enclose the string in quotation marks ("a
    string") if it contains a space or nonalphanumeric characters. A
    DCL command can contain a maximum of 1024 characters.