So if the person using the computer types the symbols into a field/box being shown on monitor N1 the symbols are then shown in a second window, full screen, on monitor N2.
May be doable via some Kiosk software. The computer and monitor N1 to control what is to be shown via a window extended to monitor N2.
Did some research but did not note any kiosk applications actually doing that: e.g., some form of "live display". Seems overly complicating things.
I believe that you can probably create the same effect via Excel without too much effort.
(Or Visual Basic, Access, Python, any programming language. Should not be difficult if you have anyone with a reasonable amount of programming experience.)
Excel:
Create a source spreadsheet with a cell or cells for data entry and a second linked Excel target spreadsheet (or page even) for display.
Open both spreadsheets, enlarge the target spreadsheet to full screen size and drag over to extended monitor N2 for fullscreen display.
Leave the source spreadsheet displayed but small on monitor N1.
Enter the symbols into the source spreadsheet using whatever fonts, sizes, colors, and emphasis you wish.
The target spreadsheet being linked would reference the source spreadsheet cell contents and display them accordingly. However you can change the fonts, sizes, colors, and emphasis and make the contents different for display purposes.
Try the concept out. Experiment some. Gives you full control over everything and you will not be dependent on some 3rd party. And free to make changes however you wish or require.
Here is the key:
https://www.wikihow.com/Link-Sheets-in-Excel
Try and work out a simple one cell to one cell test.
Get it to work (functional) then make it pretty.
Edit: Almost forgot. 7 segment fonts.
https://www.keshikan.net/fonts-e.html
Google for more choices.