The use of flowers in jewellery also had meaning. Forget-me nots meant remembrance while ivy meant faithfulness to a lover. There are accepted lists of the meanings of flowers.

A single hand carved out of ivory (see photo at the top of this post) or coral offered love or friendship while a ring with clasped hands, meant ‘Lasting Love’. Doves were commonly used to represent peace and, if carrying a sprig, hope. Snake jewellery was popular, particularly with Queen Victoria, representing infinity and eternal love. A key meant giving the key to open my heart.
Buckle rings are symbolic of eternity as the band curves around and threads back into itself. The buckle also represents loyalty and binding love when given by one person to another.

Acrostic jewelry first became popular in 1809 through some jewelry designed by the French jewelry house, Mellerio dits Meller. The first letters of the gemstones become the word of the love token dedication, like ‘regard’ and ‘dearest’.

Lockets were commonly given to celebrate an event such as a wedding or a christening or an anniversary. Many of these contain a compartment for hair from a loved one or for photos. In the early years of her marriage, Queen Victoria constantly wore a heart shaped locket containing a lock of Prince Albert’s hair.

Perhaps the most sentimental of all is the eye brooch or pendant. These were paintings of a lover’s single eye, usually then surrounded by pearls or gems. They were meant to be anonymous so that no one except the recipient knew who the giver was.
Two good references about sentimental jewellery are:
Ann Louise Luthi, Sentimental Jewellery, 1998, Shire Library
Shirley Bury, An Introduction to Sentimental Jewellery, 1985, Stemmer House