Most forums have the ability to ping someone by typing @username. They will get a notification telling them that they have been mentioned in a thread, and pinging them will also create a link to their profile.

With LD, it would work better if you used someone's ID to ping them, since usernames can be changed quite easily.

It would be much easier than having to stay subscribed to a thread until the OP replies, getting notification when anyone replies to that thread. It would also allow users to make pinglists. If you have a shop selling lions for example, people can ask to be on a pinglist for new cubs, and you can use that list to let them know, instead of PMing them or having to wonder if they subbed or not.

I think this might've been suggested before, and if so I'm sorry if this is seen as an annoyance.