VMS Help Sys Parameters, USERD2  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    USERD2 is reserved for definition at the user's site. The
    reserved longword is referenced by the symbol SGN$GL_USERD2.

    On Alpha systems, this symbol is in the
    SYS$LOADABLE_IMAGES:SYS$BASE_IMAGE module.

    On VAX systems, the symbol is in the SYS$SYSTEM:SYS.STB module.

    USERD2 is a DYNAMIC parameter.