Random thought: using serifs to encode additional bits with a Reed-Solomon would allow for, say, one bit per letter (either we use the serif or the sans-serif version). Assuming latin characters, it would allow for t/2 = 1/16 (6,25%) of the original text - a bit lower if we consider that letters like "o" do not have serifs, somewhat higher if we remove easily-guessable words like "the", "an" and so on.

That's a good idea, I might do a quick Show HN about that.