I'm not quite sure how such functionality is called, for Vanilla Forums there is an extension called Yet Another Gamification Application
that features configurable reaction buttons for rating comments.
In the end just a "Like" or "Thank" button for posting would to, it should prevent countless follow-up posting where forum members verbally thank a previous poster or the OP for the provided information (which can be really annoying).
Such function is available in most other forum software and I think it really is very useful. In addition to the above it can serve as rating for postings, to determine the top "liked" or "thanked" postings on an own summary page, like it's done with the module for Vanilla Forums on the "Best of..." page.