Random explanation time for my (one of many- 💀) self-indulgent design choices (/lh) yipeeee
I feel like the reason why Khan and Nori would be the only married drones to have an actual wedding band (and of course because that is a human tradition) is cause Nori (obviously) has been around humans for most of her life, and I like to think that (since she is a HUGE nerdy dork) she would definitely try to "research" stuff about them and find out about "cool stuff" (also she definitely would have gotten hyperfixated on the topic and started info dumping about humans to Khan lol-)
Basically what I'm trying to say here is that when Nori found out about the common human tradition of a married couple both wearing a ring, she wanted to do that kinda thing with Khan. And Khan just rolled with it because he loves her so much and would do anything to make her smile. (He loves his kooky wife <33)