Leto and Ayer already payed homage to Alan Moore and Dave Gibbons' The Killing Joke in a teaser photo released earlier this month. Now, they've done so again (though more subtly) here.
The purple glove and pose Leto is striking - gripping his head in a fit of laughter - are an homage to one of the most iconic Joker images of all time: the true "birth" of the villain in The Killing Joke.
The Joker we meet in Suicide Squad will already be well established in the DCCU, however, meaning this is likely nothing more than a clever nod to an iconic and beloved image of the famous psychopath, though it COULD give us a glimpse at the psychology that Leto will tap into for his performance.