Library /sys$common/syshlp/dbg$help.hlb DEBUG, SET, ATSIGN, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    When you invoke a debugger command procedure with the execute
    procedure (@) command, the debugger assumes, by default, that the
    command procedure file specification is SYS$DISK:[]DEBUG.COM. The
    SET ATSIGN command enables you to override this default.

    Related commands:

       @ (Execute Procedure)
       SHOW ATSIGN