A collection of well-placed Easter eggs in Titans season 3 pay homage to Batman's Batcave in the original DC comics, while also confirming the existence of several major villains. After Titans season 2's battle against Deathstroke took place upon the backdrop of sunny San Francisco, the action moves to the somewhat less sunny climes of Gotham City for season 3. This means closer looks at iconic Batman locations in live-action - Wayne Manor, GCPD headquarters, Arkham Asylum and, of course, the Batcave. Bruce Wayne's fun bunker has appeared in Titans before - though primarily as part of the Trigon dream sequence bridging seasons 1 & 2.
In Titans season 3, however, Dick Grayson returns to Gotham full-time in the wake of Jason Todd's murder, finding Bruce cleaning off his fallen sidekick's bloody outfit in the Batcave. After Bruce kills Joker (or so he says) and leaves town, the Titans then adopt the Batcave and Wayne Manor as their private super-hangout, thus depicting the iconic base in far more detail.
As Brenton Thwaites' Dick strolls into Bruce's Batcave, the entry lobby reveals a fascinating host of trinkets and trophies from a career fighting Gotham City's supervillains. There's Penguin's hypnotic red and white umbrella hanging upon the left wall. The two rows of plinths contain Mad Hatter's top hat and Harley Quinn's comically over-sized mallet, in addition to several smaller items that are trickier to make out. Towards the back, there's a giant playing card featuring an image of The Joker, alongside holographic projections of a huge coin and a dinosaur.
The dinosaur, coin and playing card will be very familiar to fans of Batman's comic book adventures. The T-Rex originates from 1946's "Dinosaur Island" story, in which Batman & Robin fought off robotic dinos created by a crazed hunter. Bruce took one home (because why not) and the Batcave interior has almost always contained a T-Rex ever since. Though often mistaken as a nod to Two-Face, the giant coin is actually from a 1947 story featuring considerably less famous villain the Penny Plunderer, who used the item as part of a trap for the Dynamic Duo. The massive Joker card Batman swiped from the Clown Prince of Crime himself. Including these three iconic decorations in Titans' Batcave pushes Iain Glen's Batman (who hasn't felt especially comic-accurate) much closer to the source material. But since a giant model dinosaur would obviously seem jarring in Titans' uncompromisingly dark and realistic world, the holograms modernize the comic trophies, easing Rex and Abe into the Titans aesthetic a little more naturally.
Bruce Wayne's mini-museum gives rare insight into the past adventures of Titans' Batman. This Dark Knight is both a semi-retired veteran and studio-obligated to appear off-screen, so viewers can only piece together his exploits through references and Easter eggs. We now know Titans' Batman faced off against Penguin, who wielded an umbrella akin to Batman: The Animated Series. This universe's Joker has his own version of Harley Quinn, whose fate remains unknown as of season 3, and the Mad Hatter Easter egg tallies with the story Barbara Gordon tells about Jason Todd "minding his language." The big coin confirms Titans' Batman faced off against Joe Coyne (the Penny Plunderer's true identity), and the dinosaur hologram suggests Bruce and Dick might've even fought Jurassic robots on a mysterious exotic island. Unfortunately, the focus of Titans means these stories will likely never be told, while studio restrictions almost certainly prevent Penguin and Harley Quinn from appearing (though Hatter is probably fair game).
Titans' Batcave adornments will undoubtedly pop comic fans, but they take on a darker meaning in season 3. Compared to his traditional persona, Iain Glen's Bruce Wayne is more self-absorbed, feeding off the superhero lifestyle in a way many of his friends(?) believe is unhealthy. The Batcave's collection of trophies prove just how egotistical Titans' Caped Crusader can be.