VMS Help MOUNT, Qualifiers, /MESSAGE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /MESSAGE (default)
       /NOMESSAGE

    Causes mount request messages to be sent to your current
    SYS$OUTPUT device.

    If you specify /NOMESSAGE during an operator-assisted mount,
    messages are not output to SYS$OUTPUT; the operator sees them,
    however, provided an operator terminal is enabled.

    Example

    In this example, an RL02 device labeled SLIP is mounted on drive
    DLA0 and is assigned the logical name DISC. The /NOMESSAGE
    qualifier disables the broadcast of mount request messages to
    the user terminal.

    $ MOUNT/NOMESSAGE DLA0: SLIP DISC