Indeed, there is a rule that implicitly encompasses bumping (see "Do Not Double Post"
here). When people don't follow it, we PM them reminding them of the rules, and if they consistently don't, we warn them.
However, as much as we'd like everyone to communicate in comprehensible English, we really can't force it. We allow freedom to use chatspeak and all, and when people don't understand what the post says, they generally ask the poster to rephrase. There also is a rule for this in Gen Chat where it happens most often- see number 6
here.
There's bound to be an influx of newcomers during plot seasons, most of which probably post before reading the rules. Happens all the time. But until a true "epidemic" has broken out, I think there's no urgency to put it up in lights. It's definitely constricting if we have to impose these rules, and I think I can speak for the staff in that we don't want the forum to feel like that at all. :)