John Winchester owned a golden wedding ring.
In 1973, John proposed to his girlfriend, Mary Campbell. This relationship was disapproved of by Mary's parents, but following their "accidental" deaths, Mary accepted John's proposal and the two got married. Their union produced two sons, Dean and Sam Winchester.
Unbeknownst to John, he himself had in fact died shortly after Mary's parents, all three killed by Azazel. Mary made a deal with Azazel, giving him permission to enter her home in ten years in exchange for John's resurrection.
Ten years after their marriage, Azazel visited their house and fed demon blood to their second son Sam, who was six months old. Mary tried to intervene, but was killed as a result and along with their family home, she was set ablaze.
The loss of his wife drove John to seek vengeance, becoming a hunter and training his and Mary's children as soldiers. In the two decades John spent searching for the demon responsible, John held onto his wedding ring, Mary's one presumably destroyed in the fire. John did sleep with two other women, but his feelings for Mary remained unchanged.
John was first shown with this ring when he returned to Lawrence and found out that Mary's ghost was haunting their former home. Touched that her ghost sacrificed itself to save their sons, John gazed at the ring tearfully.
John eventually sold his soul to Azazel when Dean fell into a coma. John's journal, along with all of his remaining possessions as well as his ring, fell to Dean. It wasn't until ten years later that Dean did The Darkness a favor and in return, Mary herself was brought back to life.Having been dead for 33 years, Mary felt lost in this new world with two adult men claiming to be the children she remembers. John's absence took a toll on Mary, and Dean handed Mary all of John's possessions. Mary took John's wedding ring and wore it around her neck.
The only time she is shown removing it is when she had sex with Arthur Ketch. Like John, Mary's feelings for John had not changed, she had simply moved on.