Further to Dr John Doherty’s letter, the difficulty of distinguishing the ironic from the literal in writing has long been recognised.
In the 17th century, the natural philosopher John Wilkins, who married Oliver Cromwell’s sister, proposed that irony should be marked with an inverted exclamation mark (¡).
In the 1960s, the French author Hervé Bazin suggested the Greek letter psi (appropriately pronounced sigh) should be used.
To substitute intonation in speech, Bazin put forward other punctuation marks to signify love, acclamation, certainty, doubt and authority. Since none of these have come into use, perhaps emojis could be used?