To Gain and to Give: Hilchot Tzedakah, Day 5
There are a number of ways that tzedakah can be distributed from the giver to the receiver. The best way to give tzedakah is when neither the giver nor the receiver is aware of the identity of the other. A less ideal method of giving tzedakah is when the giver is aware to whom he is giving, but the receiver is unaware of the identity of the giver. Less ideal than this, is when the receiver is aware of the identity of the giver, even if the giver is unaware of the identity of the receiver.
שו"ע ס' רמט ס"ז-ט'