A couple came to me for a set of two engagement rings inscribed with the Hebrew phrase וארשתיך לי לעולם (v'eirashtich li l'olam, "I will betroth myself to you forever"), because they wanted to start their engagement on completely equal footing. We decided to create rings that were stylistically different but intrinsically related to each other.
Clearly the rings are bound to each other by the phrase itself, but the relationship goes deeper. Borrowing from Chinese seal-engraving, the groom's ring is cast in relief (陽文, "yang script"), representing the male; and the bride's ring is cast intaglio (陰文, "yin script"), representing the female.
Adding to the symbolism, the two rings were made together in the same casting, so before they were cut from their sprues they started their lives as one solid piece of silver. As the rings were created as one and have become two, the couple started as two and shall become one.