Peace be upon you. Generally, if the found item is worth less than a dirham, it is permissible to keep it. If it is worth a dirham or more and does not have any identifying marks for its owner, it is obligatory to give it in charity on behalf of its owner. If it has identifying marks, you must announce it and search for its owner for a year. If the owner is found, it should be returned to them; otherwise, you may keep it with the intention of returning it to the owner if they are found later or keep it as a trust without liability. It is recommended to give it in charity to the poor on behalf of its owner at that time. A legal dirham is approximately equivalent to 2.5 grams of 22-carat silver.