This is a custom Decepticon engagement ring setting created by DeviantARTist TheBoog17. Because if there's one thing that should symbolize a lasting marriage, it's deception. No word if it transforms and rolls out into a slap bracelet, but that would make it infinitely cooler than Transformers 4 is gonna be.
Thanks to Katt, who asked for a brass knuckles engagement ring so she could get 4x the diamonds. Smart.