code: def _convert_num(self, sign):
          
          # Check if there's a number at the end
          new_sign, num = self._get_number_from_sign(sign)
          if num < 2:  # "ab" -> "ab"
              return new_sign.replace(str(num),
                                      self._convert_number_to_subscript(num))
          if num > 3:  # "buru14" -> "buru₁₄"
              return new_sign.replace(str(num),
                                      self._convert_number_to_subscript(num))
          if self.two_three:   # pylint: disable=no-else-return
              return new_sign.replace(str(num),
                                      self._convert_number_to_subscript(num))
          else:
              # "bad3" -> "bàd"
              for i, character in enumerate(new_sign):
                  new_vowel = ''
                  if character in VOWELS:
                      if num == 2:
                          # noinspection PyUnusedLocal
                          new_vowel = character + chr(0x0301)
                      elif num == 3:
                          new_vowel = character + chr(0x0300)
                      break
              return new_sign[:i] + normalize('NFC', new_vowel) + \
                     new_sign[i+1:].replace(str(num), '')
docs: Converts number registered in get_number_from_sign.
  
          input = ["a2", "☉", "be3"]
          output = ["a₂", "☉", "be₃"]
  
          :param sign: string
          :return sign: string