Can I add my own symbols to the Mac's Character Viewer?

Character Viewer just displays the characters contained in the fonts installed on the machine. To add your own symbols you have to create a font that includes them, using a font editor app.

Many symbols and characters are available to be displayed in Character Viewer.

The "secret" to finding them is to click the ⚙️ icon in the top-left corner of the Character Viewer window, then click "Customize List...". This gives you access to so many characters you won't know what to do with them all.

Be sure you add your favorite characters to the ★Favorites category on the Character Viewer main window.

I hope this is helpful.

D.I. Johnson wrote:

This gives you access to so many characters you won't know what to do with them all.

Good point! Existing fonts already support more than 100,000 characters.

Thanks for pointing that out. Now I know where those earlier Technical Symbol and Geometrical Shape lists got off too.