def symbol_chars_are_valid(symbol_chars)
  # :aaa == :"aaa" if it has valid Symbol literal chars
  eval ":#{symbol_chars} == :#{symbol_chars.inspect}"
rescue Exception
  false
end

chars_to_try =
  '`~!@$%^&*()-_+={}[]|\;:"<>,.?/'.split('') + ["'"] +
  ('A'..'Z').to_a + ('a'..'z').to_a + ('0'..'9').to_a

puts "valid as first char:"
puts chars_to_try.select {|c| symbol_chars_are_valid "#{c}aa" }.join ''
puts "valid as middle char:"
puts chars_to_try.select {|c| symbol_chars_are_valid "a#{c}a" }.join ''
puts "valid as end char:"
puts chars_to_try.select {|c| symbol_chars_are_valid "aa#{c}" }.join ''