SignatureDef

 SignatureDef defines the signature of a computation supported by a TensorFlow
 graph.
 For example, a model with two loss computations, sharing a single input,
 might have the following signature_def map.
 Note that across the two SignatureDefs "loss_A" and "loss_B", the input key,
 output key, and method_name are identical, and will be used by system(s) that
 implement or rely upon this particular loss method. The output tensor names
 differ, demonstrating how different outputs can exist for the same method.
 signature_def {
   key: "loss_A"
   value {
     inputs {
       key: "input"
       value {
         name: "input:0"
         dtype: DT_STRING
         tensor_shape: ...
       }
     }
     outputs {
       key: "loss_output"
       value {
         name: "loss_output_A:0"
         dtype: DT_FLOAT
         tensor_shape: ...
       }
     }
   }
   ...
   method_name: "some/package/compute_loss"
 }
 signature_def {
   key: "loss_B"
   value {
     inputs {
       key: "input"
       value {
         name: "input:0"
         dtype: DT_STRING
         tensor_shape: ...
       }
     }
     outputs {
       key: "loss_output"
       value {
         name: "loss_output_B:0"
         dtype: DT_FLOAT
         tensor_shape: ...
       }
     }
   }
   ...
   method_name: "some/package/compute_loss"
 }