variable in turing machine
A Turing machine diagram is a form of communication. Its goal is to describe a Turing machine &mdash; usually defined as a tuple with a specific format &mdash; in a form which is easier to grasp. As such, you can use whatever shortcut you want, as long as everybody understands what you mean. This might entail your explaining some non-standard notation which you invented as shorthand.

Your professor might have different ideas about this, but the answer I gave is valid for the working mathematician.