An apostrophe was a punctuation mark.
Some Bajoran names also had apostrophes in them, such as Ches'sarro Seeto's. In 2370, while trying to jog Rom's memory, Odo asked the Ferengi whether the mark he recalled in the Bajoran's name was an apostrophe. Rom agreed, identifying the individual (tentatively) as "Ches'so". (DS9: "Necessary Evil")