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

    Deletes entries in the process logical name table that were
    created in user mode. If you specify the /USER_MODE qualifier,
    the DEASSIGN command can deassign only user-mode entries. Also,
    user-mode logical names are automatically deleted when invoking
    and exiting a command procedure.