An apostrophe instead of ъ was sometimes artifact of using an old typewriter (1920th). One hero of literature wondered why all the words are written with ъ (wh

An apostrophe instead of ъ was sometimes artifact of using an old typewriter (1920th). One hero of literature wondered why all the words are written with ъ (where appropriate), but об'явление (an advertisement on a bulletin board in this context) was invariably written with an apostrophe. Well, many advertisements on boards was typewritten, and even handwritten advertisement started to follow this spelling, and even when typewriter was produced with ъ, this spelling persisted in this context. But it may be an urban legend. Upd: sometime this "legend" says that after the spelling reform of 1918 the ъ at the end of words was banned, this letter was forced to be removed from typewriter as well (though it may be used in a middle of words). The article on this reform in Russian Wikipedia mentions, that for the same reason ъ was seized from typographies to restrict its usage. In both cases an apostrophe was used instead. It seems these facts are consistent with each other and this particular usage of the apostrophe.