So, a Water Tribe Betrothal Necklace is, traditionally, a hand-carved piece of jewelry given by a bride-to-be’s intended. It’s clear that a very traditional theme to have is a sense of roundness. This is shown by the first four necklaces shown.
The bottom two, Bolin’s, and Kya’s, differ highly from this, making them non-traditional. Now Bolin’s makes sense in the context we’re given from the show. Eska was shown to be slightly deranged and didn’t understand that Bolin wanted to get out of their relationship. The heavy-gothic themes help to show the dread, despair, and chain-like quality Bolin must feel. Despite this though, it still features a somewhat-round centerpiece like the traditional necklaces do.
But, Kya’s is also different. We found out via Word of God that Kya is LGBTA+. If she’s wearing a necklace, does this mean that her (assumed) wife carved it for her? Did Kya carve out one similarly for her wife?
I like to assume that the design Kya wears also symbolizes how her relationship is non-traditional, just as her necklace is.
Also don’t picture Korra and/or Asami carving and giving the other a necklace.