Q: In my yeshiva, I found an envelope of cash stashed away behind some sefarim on the top shelf of a bookcase. What should I do?

A: An item hidden away in a secure place should not be touched, even if there is a siman (identifying feature). The owner clearly placed the envelope there and will presumably return to retrieve it. Furthermore, by taking it, you make it more difficult for the owner to reclaim it (C.M. 260:9-10; Shach 260:29).

Even if you picked up the envelope, you should return it promptly to its place. However, if you already took the item home and time passed, you should not return it there. Perhaps the owner came meanwhile and saw that the envelope was gone.

Therefore, since there is a siman (location and/or sum) you must publicize the item. [If there is no siman, you should hold it until Eliyahu Hanavi comes and clarifies whose it is.] (Sma 260:41,48).

However, if the envelope is dusty and seems to have been there a very long time, you can assume that the owner already abandoned hope of retrieving it (yei’ush) and you may keep the money (C.M. 262:5).