Creators of threads that have a specific question in a thread, use it to bring thread back under attention when their question is still unanswered. By simply replying to their own thread with whatever text, the thread is put in the top of a list in a forum (where is gets more attention). To clarify their intention, they usually use words like "up" or "bump" (bumping the thread up) instead of random text/characters.
Overly bumping up threads is this way is unwanted behavior, although we don't have set a limit neither have we ever acted in the past for it.