The SIGN= specifier determines the
default sign mode (for OPEN), returns the default sign mode (for
INQUIRE), or specifies the sign mode (for WRITE).
The SIGN= specifier is not permitted in an OPEN or WRITE
statement that refers to an unformatted file.
If a file is preconnected, or is opened without a SIGN=
specifier, the default sign mode is 'PROCESSOR_DEFINED'.
The sign mode determines whether the optional plus sign is produced
when writing a positive numeric value.
If the sign mode is 'PLUS', the plus sign is produced (providing it
will fit into the format field).
If the sign mode is 'SUPPRESS', the plus sign is not produced.
If the sign mode is 'PROCESSOR_DEFINED', whether it is produced or
not depends on the Fortran processor; for the NAG Fortran Compiler
this has the same effect as SIGN='SUPPRESS'.
The current sign mode may be overridden within a format by use of
the SP (sign plus), SS (sign suppress) and S (sign
processor_defined) edit descriptors.
In an INQUIRE statement, the value assigned is 'UNDEFINED' if the
file is connected for unformatted input/output or if there is no
connection.