Lovers of The Last of Us Part II know that Ellie's moth tattoo has quite a lot of meaning and history. For starters, it covers up the bite she has had since before the events of the first Last of Us game and also seems to connect her to Joel even further, as he has a guitar with the same symbol on it. Turns out, there was almost another reason for the moth tattoo that has since been discovered through cut dialogue from The Last of Us 2.
The Last of Us has lots of hidden secrets, many of which further the world and characters in subtle ways. That said, there's also lots of stuff that gets cut in the process of developing the game. This could be as simple as just removing a mechanic or weapon or it can be as big as something that informs the characters and has larger implications. Given games are developed over many years, it's no surprise the creatives change their mind on many different things, especially following focus tests.
One such piece of cut content was an exchange between Joel and Ellie, seemingly during a flashback sequence in the game after Ellie has gotten her tattoo. Ellie's iconic tattoo almost had a different backstory, seemingly involving the Savage Starlight comic that's found within the Last of Us universe. Reddit user taegukie (via Eurogamer) compiled a few pieces of scrapped dialogue from The Last of Us 2 that sees Joel asking Ellie about the origins of her tattoo, assuming it's from Savage Starlight. Ellie gives a non-definitive answer, so she may just be hiding the truth from Joel that she was inspired by the guitar, or that simply wasn't part of the story quite yet which is why this dialogue ended up getting cut.
Given Joel's death in The Last of Us 2 and the ongoing motif of the guitar throughout the story, having the moth link both characters is much more powerful than her having been inspired by a comic book. It's still sweet that Joel showed interest in Ellie's hobbies by going out of his way to read the Savage Starlight comic book and then making that connection. Although he was an extremely flawed character, his love for her was consistently strong and incredibly heartwarming.
It's unlikely Joel will make an appearance in The Last of Us 3 as it seems Naughty Dog has closed that part of the story for Ellie. Of course, there's a chance he appears in a cameo via flashback or a dream sequence, but for the most part, Ellie has tried to leave Joel behind as she left his guitar back in her abandoned farmhouse at the end of The Last of Us 2.