The idea of a ring with a drug hidden in it just reminded me of the hypodermic ring from Get Smart.
If we are going with animal jewelry, the cat from outer space has a nice collar.
I’m sure the idea of the assassin’s ring with poison hidden within/under the jewel is widespread, but I can’t think of many examples. Gets a passing mention in Discworld’s Nightwatch IIRC, but there must be more…
Poison rings were an actual thing.
Interesting! Teh article points out that back in the day it was quite difficult to get a substance so lethal the few drops in a ring would be guaranteed to kill, but I guess has it has the beneftis of subtlety.
And helpfully, that article lists uses in culture, from Asterix to Tosca and Il Trovatore.
But better than that, it also cites this 1877 monograph on “Finger ring lore” which helpfully mentions:
Solomon’s ring, which had various powers according to the teller, including healing and summoning of djinns, and was also the source of his wisdom.
The ring of Polycrates the tyrant, advised by a friend that as he was so successful in life, Fate must be storing up a calamity, and to avoid thsi he should sacrifice a favourite gem so that he could truly say life was not all roses. Some time after he threw his ring into the sea, a fisherman turns up with a spectacular catch fit only for the big man, in which of course was the ring - there’s a lot of variations on this tale.
One - this is all in the link, it’s great - is the tale of St Kentigern and the jealous husband, which parallels the Three Musketeers plot - the ring is a token of love, the husband finds it where it shouldn’t be, throws into the river and then asks the wife to produce it. All is lost until the Saint commands the biggest fish of the day’s catch to be brought to him.
Philostratus relates how Chariclea escaped unharmed from the funeral pyre on which she was condemned to be burn by the jealous Arsace, from having secreted about her the spousal-ring of King Hydsapes ; which was set with the stone called Panderbes, engraved with certain sacred letters’ and antagonistic to fire.
There’s a ton more in there, especially from medieval romances: rings that allow the wearer to speak to birds, rings that protect the wearer from harm, paired rings that obliterate and restore memory, rings that show visions of the future… thank you William Jones, FSA, your work lives on.
In the novel Starship Troopers, when off duty and out of uniform, soldiers would wear an earring shaped like a skull, with one crossbone for every mission they had participated in.
In several James Bond movies, SPECTRE agents wear jewelry (usually rings) with the organization’s logo on it.
In the movie For Your Eyes Only members of Colombo’s gang wear pins with a dove emblem.
The Akatsuki of the Naruto series all wear irreplaceable unique rings whose power and nature is never fully explained.
The Droods of Simon Green’s Secret Histories series wear golden torcs made of exotic matter that can extend over their bodies into powerful magical armor.
The shield necklaces invented by the male protagonist of Bujold’s Sharing Knife series have major plot relevance.
In Daughter of Witches by Patricia Wrede, one of the main antagonists wears a necklace with a dark crystal that links him to his “god”, which is actually a bound Shadow-Born (the Ancient Evils of the setting). It later leads to his possession.
Goodness. I never really looked at that before. It’s an unfortunate choice.
I love that example they cite in the TV Tropes image. It’s from Asterix in Switzerland, and I love that the villain (“Varius Flavus” in the English translation) has to go through several rings to find one that still has poison in it . (“I must remember to get refills!”)
For a second there, I thought I was going to have to declare a timeline breach. But no, there were two.
Melisandre’s ruby necklace in GoT which carried the glamour that made her look young and beautiful. There was another that she put on the Lord of Bones to make him look like Mance Rader.
The watch chain in The Gift of the Magi
Betan earrings in the Vorkosigan Series which signal any possible combination of sexual availability and interests. I would also argue that Mile’s vintage dagger, although functional, is also worn as an item of adornment, and might qualify.
Rowena Ravenclaw’s Diadem
Marie Antoinette’s diamond necklace “The Queen’s Necklace”, Dumas.
Daisy’s pearl necklace in The Great Gatsby
The necklace in de Maupassant’s The Necklace. 
Maybe the OP doesn’t want to count paintings, but there’s a movie based on the painting…