Blue Penguin Classics pocket paperback, well-thumbed

I lost my blue Penguin Classics pocket paperback yesterday around 3pm. It's a small pocket-sized book, about A6, with a bright blue cover and a creased spine from years of use. The back cover has a faint coffee stain and a green ribbon bookmark with a tiny brass compass charm poking out. I was sitting outside Waterstones on Princes Street, near the tram stop, and wandered toward Waverley Station, but I must have dropped it somewhere along the sidewalk between the shop doorway and the Scott Monument steps. This book is sentimental to me; it was a gift from my grandmother, and I'd really love to get it back.