The serial number seen in the software, Displax Connect, is that of the touch controller inside the Tile.
It is not the same as the actual Tile serial number, as it's an internal component of it. At present, it is not possible to use the touch calibration software to retrieve the Tile's serial number.
As it is unlikely to always have access to see the back of the Tile to see its serial number, you can add each Tile's serial number, as the label of each respective touch controller in the software, here:
You can choose whatever you want as the label for each Tile. I have attached a short video showing a feature in Displax Connect, that indicates which Sensor is being touched in a multi-interactive display setup. You will see an orange bar light up in the left pane of our software, right next to the actual sensor being touched. This make it easy to find which Tile is which, and then you can label them as you prefer.