Let's talk about where you'll spot those stern cross insignias. Sōsuke Aizen lays it out in the early Hueco Mundo arcs: the Quincy symbol represents the five-pointed star they wear, but the literal 'mark' appears etched into various places across the story. You can find it carved on the stone gate to the Quincy Shadow Realm in the manga, around chapter 480 if I remember right? It's also subtly woven into Uryū Ishida's early attire patches, and later, it's all over Yhwach's throne room and the Sternritter gear. The anime adaptation adds some extra flair, showing it glowing during Uryū's fight with Mayuri and in flashbacks explaining the Quincy massacre.
Honestly, I think the coolest appearance is when it's used as a narrative device, not just decor. That symbol turning from a badge of pride into a scar of genocide hits different on a re-read.