Q: If I left a pen or sefer in the beis medrash, or a towel in the mikveh, and saw a similar one there the following day, can I assume that it’s mine and take it?

A: If you recognize the item as yours (tevias ayin), you can keep it, even if you do not have any clear siman to positively identify it. The requirement to provide simanim is only to reclaim an aveidah from another finder (Nesivos 259:3).

If you do not necessarily recognize the item as yours, but think that it could be, some allow you to take it immediately and keep it. Others allow you to hold it but require that you wait and see if someone posts a “lost” notice.

If no one claims the item within a reasonable time, you can assume that it is the one you lost and keep it (Pischei Choshen, Aveidah 3:18[53]; Minchas Yitzchak 3:17; Hashavas Aveidah K’halachah 11:8).

On the other hand, if you recognize that the item is not yours, you may not keep it even if you lost a comparable item. (We discussed previously what to do if your item was mistakenly taken in exchange.)