Sterling silver necklace with heart pendant

I lost my sterling silver necklace yesterday around 3pm while wandering the Old Port in Portland, Maine. It's a delicate 18-inch chain with a small heart pendant; the back is engraved with an 'M,' and there's a tiny star charm on the clasp. It was a gift from my grandmother and means a lot to me, so I’m really hoping someone found it and can return it. It disappeared near the waterfront park along Exchange Street, between a row of little boutiques and the bike racks.