code: private boolean isHHSign(String str)
      {
          boolean sign = true;
          try
          {
              char r = (char) Integer.parseInt(str, 16);
          }
          catch (NumberFormatException e)
          {
              sign = false;
          }
          return sign;
      }
docs: Dmitri Ilyin: Makes sure if the String is HH encoded sign.
  @param str must be 2 characters long
  
  @return true or false