Using a star as a tag is a good enough workaround for me. On the Mac OS, you can add a shortcut to the Black Star (★) symbol by using the SysPrefs > Keyboard > Text panel. Type your shortcut - I use Tex-style shortcuts like \star. To insert the Black Star ★ in the 2nd column, open the "Emoji & Symbols" Panel (enable this menu item in SysPrefs > Keyboard > Keyboard), and double-click the symbol to be inserted. Insert it in the 2nd column, to replace your \star or whatever you chose. See the attached image for an example.