Q: What should I do with an aveidah item that I found on Shabbos or Yom Tov?

A: If the aveidah is not muktzeh and was found in a building (or there is an eruv) you should tend to it. You may even announce the aveidah on Shabbos. If there is no siman, you may take the aveidah for yourself (O.C. 306:12; Shemiras Shabbos K’hilchasah 29:32).

If there is no eruv, you may not carry the item. If there is a questionable eruv, which you generally avoid using but rely on when necessary, you should consider whether you would rely on the eruv had this been your own object (see C.M. 263:1).

If the aveidah is muktzeh, even if only a kli shemelachto l’issur, you cannot pick it up, but can move it aside with your foot to a safe place and collect it after Shabbos (O.C. 266:13).

On Yom Tov you may pick up any item that is not muktzeh. On Chol Hamoed you are allowed to write and post a sign. The owner may be visiting just for Yom Tov, so it is considered a davar ha’avud (Hashavas Aveidah K’halachah 11:3-4).