code: def get_max_drift_csig(self):
          
          old = self.get_stored_info()
          mtime = self.get_timestamp()
  
          max_drift = self.fs.max_drift
          if max_drift > 0:
              if (time.time() - mtime) > max_drift:
                  try:
                      n = old.ninfo
                      if n.timestamp and n.csig and n.timestamp == mtime:
                          return n.csig
                  except AttributeError:
                      pass
          elif max_drift == 0:
              try:
                  return old.ninfo.csig
              except AttributeError:
                  pass
  
          return None
docs: Returns the content signature currently stored for this node
          if it's been unmodified longer than the max_drift value, or the
          max_drift value is 0.  Returns None otherwise.