VMS Help TCPIP Services, TELNET, TN3270 Keyboard Functions, Logical Or  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    VT100: EXT + O              VT200: EXT + O
    DEFINE_KEY Function: (None)

    Represents the remote host's symbol for a logical OR; displayed
    as a solid vertical line from the terminal's graphics set. Press
    Ext + O if the vertical bar is not available on your keyboard.