Silver pendant necklace with heart charm

I was out in Watertown yesterday around 3pm and realized my silver necklace was gone. It's a simple 18-inch sterling-silver chain with a small heart pendant about 1 cm across, no visible brand stamp. On the back of the heart there's a tiny engraving 'Mom' and a small scratch from wear. I last saw it near the Watertown Public Library on Main Street, by the coffee shop, before I headed toward the river walkway. It has enormous sentimental value — it was a gift from my grandmother who passed away last year. If anyone found it, please let me know; I really need it back.