All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
This lost property is called Luqtah. If one year passes over announcing it and nobody claimed it then it is permissible for the finder to keep it. However, if the owner appeared and stated the features of that money then it should be paid to him. Therefore, it is incumbent upon the finder to memorize the distinctive features of that money in order to give it back to its owner in case he claimed it.
Nonetheless, if the picked up money isn`t of much value then it is not conditioned to announce it for a whole year. Rather, it suffices to announce it for a period after which it is most likely that the owner wouldn`t claim it.
As for the method of announcing the Luqtah, this depends on customary practice. If it a large amount of money then the finder has to announce it a lot and via different methods. However, if it isn`t of much value then it suffices to announce it in the nearest places to where it was found. Undoubtedly, if the owner doesn`t appear then it is safer to give it to charity. And Allah The Almighty Knows Best.