In chapter 4, Scout initially finds a piece of Wrigley’s Double-Mint chewing gum in the knothole of the Radley tree and quickly puts it into her mouth. The next gift Jem and Scout find in the knothole of the Radley tree is a tiny package, which contains two scrubbed and polished Indian-head pennies. Jem is fascinated by the Indian-head pennies and initially thinks that the knothole might be someone's secret hiding place. The reader can infer that the Indian-head pennies inside the knothole were a gift to Jem and Scout and not randomly hidden. The anonymous gift-giver wanted to make sure that both Jem and Scout received a gift, which is why he left two Indian-head pennies, one for each child. Also, the reader can infer that the anonymous gift -iver is a male because of the nature of the gift. Judging from Jem's reaction and Scout's passive attitude toward the Indian-head pennies, one can infer that the gift-giver was once a little boy who was also fascinated with Indian-head pennies like Jem. Later on, Jem has an inherent feeling that the anonymous gift-giver is their enigmatic, reclusive neighbor, Boo Radley.

The children have no idea where their treasures come from.  They find them in the tree and take them, assuming that the treasures are left there for them but with no real proof of this.  However, the gift of two pennies does provide that proof for the reader.  Whomever is leaving the items must be clearly targeting the Finch children - the two Finch children, as well as the only two children on the street.  This lets readers know that the gift-giver has some knowledge of the children, as if he is watching them and providing things he knows they will enjoy.