Green paperback mystery novel with distinctive marks

I found a green paperback mystery novel this morning around 9am outside the Merced Library on 21st Street. The cover is bright green with a silhouette of a detective, and the spine shows a crease from being shelved and reread. The title reads Shadows on Main, and there are dog-eared pages around chapter 12. On the back cover there’s a pale blue sticker with the initials 'J.S.' and a small pencil note that says 'Merced Book Club'—two distinctive marks that might help identify it. It’s in decent shape overall, just a bit worn from daily use.