[img]https://cdn.discordapp.com/attachments/428770040276582400/519345176326438932/unknown.png[/img]

I don't know if this is what you're looking for, but RPG already tracks what threads you've looked at. Those that you've clicked on are no longer bolded in the list. The green dash indicates threads you've posted in.

You can always subscribe to the thread for later viewing, too, if that was what you were implying in a "mark forums read" thing.