Problem regarding Turing Machine notation
Unless I'm misunderstanding the diagram, the way to replace it is with a transition for every letter in your tape alphabet.

Say your tape alphabet $\Gamma = \{ 0,1,2,3 \}$, plus the blank symbol. Then you would have a transition from $R$ to $La$ when reading 0, another when reading 1, another when reading 2, another when reading 3, but NOT one when reading a blank.

You are right in your intuition that this is just syntactic sugar. What it is really doing is using one transition to represent several.