'Returns the \'s3\' (sigv2) signer if presigning an s3 request. This is
intended to be used to set the default signature version for the signer
to sigv2.
:type signature_version: str
:param signature_version: The current client signature version.
:type signing_name: str
:param signing_name: The signing name of the service.
:return: \'s3\' if the request is an s3 presign request, None otherwise'

def _default_s3_presign_to_sigv2(self, signature_version, **kwargs):

    for suffix in ['-query', '-presign-post']:
        if signature_version.endswith(suffix):
            return ('s3' + suffix)
