You can create a "Dealer" label by editing the table blueprint (XML) file. For example, insert the following into one of the racetrack blueprints included with the software:
<label>
<location x="center" y="0" />
<text>Dealer</text>
</label>
Make sure it is within the <table> section. You can play with the x and y values "in real time", meaning you can modify the file while the Seating Chart screen is displayed. After you make changes, just press the hotkey (F4 by default) to go to the Seating Chart page (even though you're already displaying the Seating Chart page, this will tell the TD to redraw everything) and the TD should recognize that you've made changes to the file and re-render the screen.
You should probably make a copy of the blueprint file and edit the copy. If/when you install an update to the software in the future, it will overwrite included templates and blueprints, so you'll lose your changes if you edit the included file.