Snow's engagement ring

Snow's engagement ring is a ring that once belonged to Ruth, who later gave it to her son, David so that he could use it to marry the woman he loves. Snow White thus becomes the owner of the ring.

Before the Curse
Ruth wears the engagement ring when she's met by Anna, who helps her and David defeat Bo Peep. When David is taken away and forced to marry a woman he doesn't love, Ruth gives him the ring in hopes it'll bring him love. While David, under the alias of James, is riding with his fiancée, they're ambushed by Snow White, who steals the ring. She sells it to some trolls, but after being captured by David, whom she names Charming, she helps retrieve it. When Snow tries on the ring, Charming feels a strange connection towards her. After Snow is put under the sleeping curse, Rumple enchants the ring for Charming so it will glow when near her. After their wedding, Snow wears the ring after she and Charming unknowingly banished Maleficent's child to protect their own and she begins to feel guilty.

Early History
Soon after Mayor Mills adopts a baby boy by the name of Henry (who is in fact Mary Margaret's grandson, not to anyone's knowledge at this moment in time), Regina takes the boy to the town hospital, where Mary Margaret, who is wearing the ring, is volunteering, to be checked over by Dr. Whale. She is upset because the baby won't stop crying, and believes that maybe the answer behind this apparent affliction is in Henry's genetics. As she's calling Sidney on her cell to look into the child's birth mother, she hands Henry to Mary Margaret, who cradles him in her arms. When she does so, he stops crying, much to Regina's shock, and the Mayor tries holding her son in the same way Miss Blanchard just did. However, he continues to cry, and Mary Margaret apologizes to the upset Regina for she believes she's done something wrong. Regina tells the teacher that she's done nothing, and takes Henry home, beginning to worry that she may just be a bad mother.

Season 1
Mary Margaret, unaware of the rings origins, wears it when she visits a comatose David and later when she finds him after he goes missing. After Emma moves into her loft, she wears the ring when Mr. Gold visits. Mary Margaret continues wearing the ring when she visits David at the hospital to keep him company. After falling for David, quitting at the hospital and being warned that she's a home wrecker by Regina, Mary Margaret wears the ring when she goes to meet David. When he stands her up, she goes to the diner and is met by Dr. Whale. She wears the ring when she's met by Graham, who is starting to remember his past life. She wears the ring when she comes home to an upset Emma. She later wears it as she puts up fliers. Mary Margaret wears the ring when Emma brings two orphans into their home. Later, she wears the ring when Emma's baby blanket seems to trigger a memory. She later wears the ring when she rescues and releases an injured dove.

Mary Margaret wears the ring when she meets with Emma and then shortly later when she goes on a date with David. She wears the ring to a girls night out with Ruby and Ashley, and later when David gives her a valentine's card meant for Kathryn. She wears the ring at the diner as she discusses August with Emma. Later she wears the ring when Kathryn confronts and slaps her at school. The ring is worn when she tries to sign up people to help for Miner's Day. After Kathryn goes missing, Mary Margaret wears the ring when Emma tells her she's a suspect in the case. She wears the ring when she's brought to the sheriff's station for her mug shot. The ring is then taken off her before she's placed in her cell. After being released from her cell, Mary Margaret is given her ring back and she wears it at her party. She later wears the ring when August installs a new lock in her loft. She wears the ring when she scolds Emma for kidnapping Henry. Mary Margaret wears the ring as she reads to a comatose Henry.

Season 2
After the breaking of the Dark Curse, Snow wears the engagement ring as she catches up with her long lost daughter, is attacked by a Wraith and accidentally sent to the Enchanted Forest. Having been found by Mulan and Aurora, Snow wears the ring as she's taken prisoner by them and taken to their Safe Haven, where she's thrown in a pit. She later wears her ring when she goes on a mission to her old home to find the Magic Wardrobe. Snow wears the ring when she returns to the Safe Haven and finds Killian Jones. When Emma and Hook climb a beanstalk, Snow wears her ring as she waits down below with Mulan and Aurora. She later wears her ring after Aurora wakes up from a dream she shared with Henry. After Aurora is kidnapped, Snow is forced to visit the Netherworld to contact Storybrooke. While she does this, she wears her ring. Snow later wears her ring when she battles against Cora and Hook, eventually defeating them and making it back home. After Archie's apparent murder and Regina becomes the main suspect, Snow wears the ring as she helps find out the truth.

Season 4
Snow wears the ring when Cruella cuts her hand in order to resurrect Maleficent.