HotDamn, my friend had a pendant made.
I'm not all that fond of the "engagement ring as contract" idea either - but not so long ago, women
were viewed almost as property. Women were supposed to get married - if you weren't married by a certain age, you became a spinster and a burden to your family.
An engagement ring was a way for a groom to say to his intended, "I want to marry you, and I'm serious" - so the bride would feel secure in telling other suitors that she was unavailable. If her fiance then bailed, at least she had the ring.
Interesting tidbit along these lines: In Judaism you are supposed to have a plain wedding band, no gemstones. This is so that there can be no misrepresentation of the value of the ring (diamonds vs. CZs etc). The rabbi who performed my wedding took this one step further and forbade us from even wearing our engagement rings during the ceremony.