Grey Herschel backpack with orange zipper

I lost my grey Herschel backpack yesterday around 3pm near the Grand Arcade entrance on Market Street in Cambridge. It's a medium-sized backpack in grey canvas with an orange zipper and a slightly worn bottom edge from daily use. There’s a blue enamel frog keychain attached to the zipper pull, and inside I keep a yellow Post-it with my initials A.F. plus a few lab notes from a student project. It also holds a small photo of my grandma and a silver necklace that was a gift, so it has sentimental value and I really need to get it back. If you found it, drop me a note here.