It may well have been a file done up to look like a pocket watch fob knife, perhaps on an inexpensive pocket watch chain. This link shows some watch fob knives and the style seems roughly the same. https://www.google.com/search?q=wat...qt_WAhUJwYMKHZlSAjwQ_AUICygC&biw=1680&bih=917 They were a popular addition to a fob chain.