In the dialog box hold the Alt key and type on the number pad 0174. Don't use the number keys at the top of your keyboard.
As soon as you let go of the Alt key the symbol will display.
You may have to change the Width factor of the text. On my computer the circle comes in as an oval. 1.25 seems to work for me.
Pick on the Note Spelling Errors check.
It should display the symbol. Select it and pick the Add to Dictionary button.
Now you can copy that config file to use as your system file. Assuming you use it to distribute to everyone through your startup script.
But be careful. You can't just open the file, copy the line, and paste it in another file. It won't work. At least not on my system. I can copy the whole file or I can even open the file in notepad and save as to the other file.