engagement ring

kihlasormus A ring given to one's fiancé or intended fiancé, signifying a promise to wed, typically a gold band with one or more diamonds or other precious stones.
By extension, any ring that has the appearance of a ring given as a promise to wed.
2010, Donald L. Maly, Oasis of Hope, page 20:

After about five minutes we dug up an old engagement ring.

Wednesday: I found an engagement ring on the beach this morning, beautiful little thing, a diamond the shape of a teardrop and two clusters of tiny sapphires on either side.