WESTBOROUGH, Mass. -- Imagine getting off the train after work and finding a $15,000 diamond ring in your car.

A Northborough, Mass., man said that's what happened to him.

It seems the ring was left by a total stranger, heartbroken over a lost love.

The ring came in a box topped with a white bow. A note with it read: "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."

The finder told police about the ring after having it appraised.

Police said they have no idea where the ring came from or who left it. For now, it's finders, keepers.

"It's the time for giving, but we've never had anything this large, this anonymous, or this random," said Westbrough police Lt. Paul Donnelly.

While the incident might tempt some people to leave their cars unlocked, Donnelly warned against that.