DC Universe's Titans paid tribute to The Dark Knight Returns comic by dropping a name of some importance in comic book history: Corto Maltese. Curiously, Titans used the name in question in an entirely different manner than how other DC Comics adaptations have utilized it in the past.
The central plot of Titans season 2, episode 10, "Fallen" focused on Dick Grayson, as he was incarcerated in Kane County Correctional Facility after assaulting a federal air marshal. He did this as a personal penance, wanting to punish himself for his role in causing Jericho Wilson's death. The guard who processed Dick's paperwork noted that he was a former police detective and tried to recruit Dick as a prison-yard snitch. When Dick turned down his offer, he arranged for Dick to share a cell with the worst of the worst - three members of a gang known as the Corto Maltese.
The Corto Maltese name may sound familiar to some Titans fans. Corto Maltese was also the name of an island nation in The Dark Knight Returns, which became the center of an intentional incident similar to the Cuban Missile Crisis. This name in itself was a tribute to the titular hero of a series of graphic novels about a mysterious sea captain and soldier of fortune known only as Corto Maltese. Written and drawn by the legendary comic book creator Hugo Pratt, the series was reportedly a major influence upon the writing and art style of Dark Knight Returns author Frank Miller and is still widely regarded as one of the best Italian comic book series of all time today.
Since then, the name of Corto Maltese has been utilized by various DC Comics properties whenever a name was needed for a fictional nation in Central America or South America. It was the name of the country whose revolution Vicky Vale became famous for chronicling in Time Magazine in the 1989 Batman movie. A country called Corto Maltese has also been mentioned on both Earth-1 and Earth-38 in the Arrowverse. The Earth-1 version is where Thea Queen trained in the assassin's arts under the tutelage of Malcom Merlyn between season 2 and season 3 of Arrow. In the world of Supergirl, Corto Maltese was the site of a genocide organized by mercenary John Corben, who would later become the first Kryptonite-powered cyborg known as Metallo.
It is unclear if the gang took their name from the country of their birth or if there is some other reason for the Dark Knight Returns nod. In either case, it seems unlikely to come up again, as the only reason for the characters' existing in the first place was to help facilitate Dick Grayson's transformation into Nightwing. Still, Titans' utilization of the Corto Maltese name is an interesting change of pace, even if there is little reason behind it.