Popova surveys the many failed attempts:
This raises the necessary question of what it is, exactly, that makes representing irony typographically so catastrophic. As someone who finds even the use of italics for emphasis, with very limited exceptions, a mark of weakness of style — if a writer can’t wield language in a way that produces organic emotional crescendos, how pitiful to try forcing those typographically — I see the answer as obvious: Irony thrives on an implicit juxtaposition of contextual intention and literal meaning, so as soon as we make it explicit, it stops being ironic.
Perhaps ironically, a separate crusade for a textual signifier of irony comes precisely in the form of a script — a reverse-italics typeface called Ironics, attributed to the iconoclastic journalist H. L. Mencken, who believed Americans were unable to recognize irony and thus needed a special typeface to indicate that the writer was being facetious.
(Image via The Narrative Breakdown)