BOSTON (Reuters) -- Are diamonds really forever?

An anonymous gift-giver left a $15,000 diamond engagement ring to the owner of an unlocked car in western Massachusetts with a typed note hinting at a broken heart.

"Merry Christmas. Thank you for leaving your car door unlocked. Instead of stealing your car I gave you a present. Hopefully this will land in the hands of someone you love, for my love is gone now. Merry Christmas to you," the note said. (Watch footage of the diamond ring -- :40)

The three-diamond ring with a white-gold band appeared on the seat of the man's car at a train station in Westborough, about 30 miles west of Boston, on December 7, police said. Four days later, the man reported it to police.

"This appears to be random," said Westborough Police Lt. Paul Donnelly. "I think there was a search for a car that was unlocked."

The 37-year-old man decided to keep the ring after a jeweler appraised its value at $15,000, police said.