Not something I've ever looked for, but I just saw this mod a little farther down:
https://vborg.vbsupport.ru/showthread.php?t=267329
I don't know how SMF keeps track of things but in vb they're called 'subscriptions' and the admin can set default sub behavior, but then the user can modify it as well.
Also I think by default vb shows icons that indicate you've posted in a thread, so if someone selects "New posts" their own should be obvious.