code: def is_valid_signature(signature_def):
      """Determine whether a SignatureDef can be served by TensorFlow Serving."""
      if signature_def is None:
          return False
      return (
          _is_valid_classification_signature(signature_def)
          or _is_valid_regression_signature(signature_def)
          or _is_valid_predict_signature(signature_def)
      )
  
imports: from tensorflow.core.framework import types_pb2
  from tensorflow.core.protobuf import meta_graph_pb2
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor
  from tensorflow.python.framework import tensor_util
  from tensorflow.python.saved_model import signature_constants
  from tensorflow.python.saved_model import utils_impl
  from tensorflow.python.util import deprecation
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 8 for calling a global function with example usage: is_valid_signature(signature_def) and returns: unknown, False