[stephencanon]

> at which point exactly did diamond rings replace gold wedding bands as the "official marriage signs" in the States.

They didn't. Wedding bands are still the "official marriage sign". Diamond engagement rings are extremely common, however, and it's very common for American women to continue wearing their engagement ring alongside their wedding band.

(As with my wife and my mother, it's definitely not unheard of for women to wear just the wedding band either).