It is in Chapter 15 that Pearl constructs her own Scarlet Letter, which is formed from fresh green plants, to wear upon her own breast. This triggers of a discussion between Hester and Pearl about the significance of the letter "A". Hester draws back from explaining to the seven year old the intended meaning of the stigma, which curiously makes her feel as if she has been false to the letter.
Consider what the text says about the "A" that Pearl fashions:
She inherited her mother's gift for devising drapery and costume. As the last touch to her mermaid's garb, Pearl took some eelgrass, and imitated, as best she could, on her own bosom, the decoration with which she was so familiar on her mother's. A letter - the letter "A" - but freshly green, instead of scarlet! The child bent her chin upon her breast, and contemplated this device with strange interest; even as if the one only thing for which she had been sent into the world was to make out its hidden import.
Interestingly, and perhaps ironically, Pearl tries to "decode" the symbolism of the scarlet letter herself with great intensity. Clearly the fact that Pearl has fashioned her own "A" out of eelgrass to form a green letter, instead of a scarlet one, confirms her description as an "elf-child", a character who seems more at home in nature than in the "civilised" town. She is confirmed in the novel as a character of the world of romance, and is an incarnation of physical pleasure and imaginative freedom, entirely contrary to the Puritan way of life. This "A", therefore, highlights a key theme in the novel, which is the way in which symbols can be ascribed or imposed on others, but how then they can be reinterpreted to symbolise other things. Just in the same way that Hester re-interprets her "A" as a sign of honour, shown by the care with which she embroiders it, so Pearl takes the sign of shame and uses it to symbolise her own position as an outsider in the community, as one who is of nature rather than of civilisation.