The only characters needed to write Fortran programs, and the only ones that should be used in portable software, are those in the Fortran character set:
Although this character set is somewhat limited, it is at least
universally available, which helps to make programs portable. What
suffers is program legibility: lower-case letters are absent and it is
necessary to resort to ugly constructions like .LT. and .GT.
to represent operators like < and >. Some of the special
characters, such as the asterisk and parentheses, are also rather
overloaded with duties.