In the "Adventure Background" introductions in the mods, some or even much of it could prove perfect in response to a player's Knowledge History/Etc. Check at the start of a new campaign -- about the local area, past history of a "curse" or key historical figures etc. I've seen other layout ideas similar to this, such as in RotRL when the text references back to the Adventure Background. But what about this:
From a Creative Direction standpoint, running a vertical shaded bar in the margin with "KNOWLEDGE HISTORY DC 20" etc. in a margin-based rectangle that is flush or offset from the justified text. It would only appear where knowledge could safely be shared. It would help the DM save time in prepping and assist in communicating with players who either request the check, or with DMs who want to divulge that knowledge.
Just a humble suggestion which has probably already been done before a million times and I am sure I will be quickly humbled by someone who knows far better than I. :)