Cull Obsidian's highly talked about sash in believed to be a Captain Marvel tease.
This thought arose from the scene in New York where Cull Obsidian and Ebony Maw Infinity War Easter egg was just an optical illusion and the sash is actually orange, grey, and purple. While the colors don't match, the reasoning for it hanging from his belt was spot on.
Related: Thanos’ Black Order Were Avengers: Infinity War's Weak Link
In The Art of Avengers: Infinity War, artist Wesley Burt explained his design for Cull Obsidian and the significance of his unique look. He mentions that parts of his clothing are "custom add-ons and trophies or medals" for his years of travel and conquest. All of these fights have taken a toll, which is why he has a shoulder plate on his right side, but Cull Obsidian has also fashioned several accessories to show off his accomplishments, and the sash is one of them.
"I also brought in the hanging sash from his belt as a sort of award or honor from defeating a great foe in a previous epic battle."
The sash and shoulder plate are ways Marvel found to add character and backstory to Cull Obsidian and the other Children of Thanos. Other designs Burt did for the weapons expert of the group had him hang a collection of skulls from his belt, while also attaching the jaw bones of defeated opponents on the shoulder plate. The sash isn't as intimidating as these alternative designs, but that could change if it's ever revealed who this "great foe" is.
Now that it's confirmed the intent of the design is for Cull Obsidian's sash to be an award of some kind, many will begin to wonder who he defeated. Considering he is currently dead thanks to Wakanda's protective shield, audiences may not find out anytime soon. Any such reveal would have to take place in a movie set before the events of Infinity War, so (for instance) it could be tied to The Eternals. The Children of Thanos didn't receive much of development in Infinity War, after all, but the flashback to their conquering of Zen-Whoberi (Gamora's home planet) showed they've been with Thanos for several years, so there are stories to tell.
Of course, the sash being viewed as an award was not actually established in the movie and could just be Burt's reasoning for including it. Whether or not Kevin Feige and Marvel Studios as a whole have accepted this backstory as part of the official canon remains to be seen. If it is ever explained, then great, but if not, it'll just leave fans with one more item to theorize about with Avengers: Infinity War.
