#something generic

      ❛ everyone’s out celebrating. ❜

I would say now, in Legion present, it’s used as the Nightborne sigil, in much the same way that the Kaldorei and Shen’dralar have their own symbols on their own flags. However, the symbol’s origins were probably pre-Sundering. The flags are found in Suramar, however as you said, they’re also found in Azsuna ruins, which are from before the Sundering. Azsuna was outside of the magical barrier keeping Suramar and the Nightborne isolated, meaning the symbol could not have been novel to the Nightborne.

Because the Nightborne were the former Highborne residents of Suramar, I would have said that maybe this was a symbol for Suramar, or the ‘Court of Suramar’ that they simply adopted post-Sundering, but the symbol is also in Azsuna. Azsuna belongs to a completely different court - the Court of Farondis, which has a symbol of its own. (The tabard for the reputation simply shows a crown). It perhaps could even be Azshara’s in the sense that a kingdom will sport the symbol of its ruler, but if you look closely enough at the Well of Eternity dungeon, you’ll realize Azshara and the Eternal Court have their own symbol that looks something like a cross between an eye and a moon.

The same symbol is on some icon images, too.

 Although I couldn’t find a picture, I think the Legion archaeology tab for Highborne has that symbol and many of those archaeology items are pre-Sundering finds. Furthermore, one of those archaeology items, ‘Pre-War Highborne Tapestry’ has the symbol in its icon. Actually, all of these hanging flags could have been precisely just that - pre-war Highborne tapestries. Therefore, the symbol may as well have been a generic Highborne sigil.

Thanks for asking! :D

Edit: Totally a small detail, but in some cases, what I assume to be the crescent is closed and in some cases it’s not. The images used in this post depict a closed crescent (can you even call that a crescent?) but here’s a flag with it open: