The Filthy Coin is an item that Henry Townshend obtains in Silent Hill 4: The Room. The coin is inside a small toy box in the northeast subway car on the Lynch Street Line platform. The toy box must be unlocked using the toy key.
The coin is noted to be caked with dust and possibly too filthy for use. After cleaning the coin in Henry's kitchen sink, it is revealed to have a mark loosely resembling a 1$. The same mark appears on a vending machine on the Lynch Street Line platform, indicating that only that coin can be used.