Charm from Latin carmen 'song' originally meant 'a verse said or sung to avert some supposed bad event' (14th century), cf. incantation. Later, it meant 'amulet, talisman'. Later (in the 16th century) it meant 'some pleasing quality', and in the mid-19th century it came to mean 'a small ornament attached to a watch or girdle'. First citation for the final meaning is a novel, LKook Before You Leap (1865) by Mrs Fannie Alexander [nee French, an Irish writer, 1825-1902], (link to later edition).
Quote:
"How do you know?" asked Sir Frederic, laughing, and picking up a small charm in the shape of a heart, formed of malachite and gold, which, in nervously playing with, Miss Delvigne had detached from her chain.

Ceci n'est pas un seing.