VMS Help MACRO, VAX MACRO Assembler, Operand Formats, Immediate or Literal  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    In both immediate and literal mode,  the  literal  specified  is
    the operand.   In  immediate mode, the operand is stored in a byte,
    word, or longword following the operand specifier.  In  literal
    mode,  the operand specifier is the operand.

    #literal

    The assembler selects immediate or literal  mode,  depending  on
    the value of the literal.

    ^I#literal

    This forces immediate mode.

    ^S#literal

    This forces literal mode.  The  value  of  the  literal  must  be
    an integer  in  the  range  0  through  63,  or  one of a limited
    set of floating-point numbers.