In Joker of Todd Phillips is a clear reference to the interpretation of Heath Ledger that no one had noticed so far to the movies, despite the large crowds that surrounded the work DC Films.
Now that it has become the most profitable cinecomic of all time – and a contender for the awards season after the Golden Lion in Venice 2019 – the film is benefiting from the release of the home-video edition to attract new audiences, or to attract to if the cinema-goers: and through the more in-depth look at Phillips’ film granted by home viewing, new and interesting Easter-egg revelations and other references are also emerging.
A particular theme in Joker that DC fans have been quite satisfied with is the multiple references to other interpretations of the character. The one with whom you have chosen to pay homage to the legendary test of Heath Ledger will The Dark Knight Chris Nolan, however, is especially hidden, and has to do with an ambulance.
As you can see in the post at the bottom of the article, the back of the Gotham City ambulance refers to the character design of the 2008 film: the aster-egg is particularly witty, given that it also refers to the iconic scene in which Joker demolishes Gotham General Hospital while dressed as a nurse.
Have you found other references? Let me know in the comments.