def write_sig(self):
        '''Write signature to sig store'''
        if not self._md5:
            self._md5 = fileMD5(self)
        with open(self.sig_file(), 'w') as sig:
            sig.write(
                f'{os.path.getmtime(self)}\t{os.path.getsize(self)}\t{self._md5}'
            )
Write signature to sig store