Crafts that can be worn in adventurer mode are considered jewelry, these include amulets, crowns, bracelets, earrings and rings. Jewelry provides no protection in combat and is only for show. With the exception of crowns wearing jewelry does not interfere with wearing other items.
 Types of Jewelry
Amulets are worn on the head, presumably this models things worn around the neck in the real world like necklaces. The equipment limit is not known.
Crowns are worn on the head. Only one crown can be worn at a time. They are the only kind of jewelry that interferes with wearing other items. A crown may be worn on top of a helmet as of version 0.34.08. A crown may occasionally deflect attacks directed at the head (as evidenced here).
Bracelets are worn on the hands. The equipment limit is not known.
Eleven earrings can fit on each ear. Earrings will be put on the right ear until that ear is full and then on the left ear.Verify
Rings can be worn on the fingers and toes. Eleven rings can fit on each digit. Rings will be put first on the thumb, right hand until that part is full then on thumb, left hand, then on first finger, right hand, then on first finger, left hand, and so on. Once all the fingers are full rings will be put on the toes starting with the first toe, right foot, up to a total of 220 rings.
Sometimes during world generation when one historical figure kills another historical figure that figure will be wearing a piece of jewelry made from the figure it killed when you encounter it in adventurer mode or fortress mode. For example the goblin general leading invaders to attack your fortress might be wearing a +dwarf tooth ring+ from the hapless dwarfish soldier he struck down fifty years ago. Or while in adventure mode you may meet an elf wearing a -human hair crown- from the peasant it killed and ate over a century ago during a war over the eating of sapient creatures. The trophy behavior is controlled by an ethics tag in the entity raws.