Simon Griffin, writing in Fucking Apostrophes, [Icon Books, London, 2016] observes that ‘Geoffroy [sic] Tory is considered one of the people responsible for introducing it [the apostrophe] to the French language in the 15th century’ (p.16).
A disputable claim given that Tory’s Champ Fleury wasn’t published until 1529. Nevertheless, turning to that volume, Tory himself writes: ‘…if it should happen that one has occasion to write in Attic letters such verses, wherein the S should disappear, one may write them clearly & wittingly without putting the said letter S where it might be lost, and put an apostrophe over the place where the S should be. This apostrophe, being above the line at the end of a word, signifies that some vowel or an S has been dropped because of the metrical quantity of the vowel that follows it in the next syllable or word’ (trans. George B Ives, Dover edition, 1967, p.138).
Tory elaborates on the letter S itself, noting its Greek origin and that it makes ‘a hissingsound, of the same quality that red-hot iron makes when it is dipped in water’ (ibid, p.139). He goes on to note how a letter S (sigma in ancient Greek) represents silence ‘…for which reason the ancients often wrote it alone above the door of the place where they ate and drank with their good friends; in order to put it before their eyes that such words as they should speak at table must be spoken soberly & listened to in silence; which cannot be if there be excess in eating and drinking, which are things not meet for decency at table & for pleasant company’ (ibid, p.139).