The #Joker enjoys committing crimes because it makes him feel that he exists. Before his first crime, he was treated in a way that he doubted whether he really existed.
Therefore, the Joker, in this artwork, is linked to the well-known statement "Cogito, ergo sum" of René Descartes, translated into English as "I think, therefore I am."
Descartes, in his search to discover whether we can actually know anything for certain, realized there is at least one thing that cannot be doubted which is that he exists as he was the one doing the doubting in the first place. ⠀