A coin in the tzedakah box is or may be worth more than face value. May it be exchanged for a coin at face value?
Related question: Must an effort be made to find the original donor, e.g. hang a sign in shul?
If the coin is worth more than its face value – say, it is a silver coin – it cannot be exchanged for a coin at face value. It can be exchanged for its true value, and this should be done if possible, because otherwise “charity” will lose out. If converting the coin to its true value involves effort, the person doing it can take an accepted “commission” for doing so.
There is no need to make an effort to find the owner, which can’t be done anyway (there is no siman on a coin). Rather, the coin belongs to charity.