title: How to Write Input_Signature's for function's and model's names when using tf.fucntion?
body: <p>I want to decorate tf.function unto my training function</p>
  
  <pre><code>@tf.function
  def trainOneSample(data, model, optimizer, lossFunc, accFunc):
  ...
  </code></pre>
  
  <p>where data are a pair of 5D arrays with float32 and uint8 types (for input and label), model is the name of my NN model, optimiser is the name of an optimisation object, lossFunc and accFunc are names of custom functions. How can I decorate them in tf.function by Input_Signature? I cannot find out any solution in tf's tutorial or guide.</p>