Should a person who has dropped something from their pocket be alerted?

You should have alerted the person who dropped something, as this falls under the obligatory advice to Muslims, based on the Prophet’s (peace be upon him) saying: “Religion is advice.” Although the moment has passed, you should seek forgiveness and strive to advise and guide Muslims to what benefits them and wards off harm from them. This includes teaching them matters of their religion, preventing harm from them, enjoining good and forbidding evil with gentleness, showing compassion towards them, loving good for them, and hating evil for them.