Chao and his linguists on the National Languages Committee spent the better part of 1925 and 1926 doing something that still strikes me as sensible: instead of hanging a mark above the vowel, they put the tone inside the spelling. Change the letters, change the tone. Lin Yutang was the one who first proposed it that way. The Nationalist government made it official in 1928, and the thing got called Gwoyeu Romatzyh, which is itself spelled in its own system, like a shop with its name painted in the typeface it sells.
I care about this for a bookseller's reason, which is that accents fall off. Not metaphorically. In cheap printing the diacritic is the first casualty — the sort that breaks, the compositor who hasn't got the right piece in his case, the paperback reprint where somebody just quietly dropped them all. I have two copies of a phrasebook from the fifties; one has its marks, one doesn't, and only the loved one kept them. A tone written into the letters can't be knocked off in the press.
Gwoyeu Romatzyh mostly lost to Pinyin, but one of its spellings is in every atlas you own: Shaanxi, doubled a, kept precisely so it doesn't collide with Shanxi next door. A whole system reduced to one province's worth of survival, still doing its job. Since it's the European Day of Languages I'll allow myself the digression across the continents. There's a studio family portrait attached, the older man seated in front in his suit and glasses, the young ones standing behind in high collars.
Shaanxi is my favourite piece of survival in the whole atlas — Pinyin had no way to separate it from Shanxi, so it just borrowed the old tonal spelling and kept walking. One doubled vowel doing the work of an entire abandoned system.
The shop with its name in its own typeface — that's how scribes signed colophons too, showing off the hand they were selling. And two years of committee for one vowel sounds about right; I've read minutes where a council spent longer than that on a single preposition.