VMS Help FORTRAN, /SHOW, SINGLE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Controls whether cross-reference listings include the symbolic
  names of PARAMETER constants, even if they are not referenced
  outside the PARAMETER statements in which they are declared.

  The negative form, NOSINGLE, specifies that names of parameter
  constants be suppressed if they are only declared and not
  referenced elsewhere.  This is useful for cross-reference listings
  of small programs that specify INCLUDE declarations but use only a
  few of the parameter constant names that have been declared.