I have added this.
Twitter-style @ 'Mentions': Typing @Username produces a 'Mention' that will notify the user to your post, and also link to their profile.
eg. Type @
James in a post. (Make sure you get the username right or the wrong person would get the alert).
Quote Notification: Members you quote will be notified.
Mentions and Quotes will appear in a new tab on your User Profile (click on your username).
You should get notifications for @ mentions and quoted posts in the same place you get PM notifications.
You'll get browser notifications (if you accept them from this site).
You'll get an e-mail notification for @ mentions but not quoted posts - I turned that off. UPDATE: Disable Mention Emails' is now selected as a default option so If you want to receive emails when you are @ Mentioned go to (on desktop browser) User CP or Site Navigation (on mobile) - Settings under User Tagging and deselect 'Disable Mention Emails.
I'll try to add Android and iOS mobile notifications at a later date also.
UPDATE:
I've added extra options so you can turn all the alerts and notifications off should you want to.
On Desktop browser -
Go to User CP (top-left of screen) - Settings under User Tagging (at the bottom-left).
Then you can select 'Hide Mention Alerts' and 'Hide Quote Alerts' to turn of the PM-style notifications on the forum. You can also 'Disable Mention Emails' and 'Disable Desktop Notifications'.
On Mobile browser -
Go to Site Navigation (with the 3 horizontal bars), then User CP, then scroll down to the bottom and press Setting under User Tagging.
And select the same options above.