The Notebook (symbol)
Harriet's notebook is the book's most prominent symbol. It represents Harriet's unfiltered mind—the knowledge she gleans from spying and observing the world around her, as well as her thoughts and interpretations as they come into her head. When the notebook is stolen, Harriet feels like she has lost a part of herself, since this object is an extension of her own mind.
Mr. Waldenstein's Delivery Bike (symbol)
Mr. Waldenstein's delivery bike is a symbol of his new, happier life, after he renounced his material wealth and decided to live simply. It is modest, but it is all he needs to get around and accomplish his daily goals. He allows Ole Golly to ride on it with him, which is symbolic of his inviting her into her life through marriage.
Ole Golly (symbol)
Though she plays a far more important role in the novel than only this, Ole Golly is a symbol of Harriet's childhood. When Ole Golly was around, Harriet had someone to care for her and advise her, someone to comfort her when things went wrong and solve many of her problems for her. The moment when Ole Golly departs is a sign that Harriet must grow up, because the woman who was so emblematic of her childhood is no longer there.
The Purple Socks
Until his classmates take the time to get to know him as a person, The Boy With the Purple Socks's purple socks represent his identity as a whole. He is known for nothing else, and Harriet thinks of him only in terms of his socks. Later on, they learn his real name, and the socks eventually become just one small part of his identity, rather than a symbol for all of it.
The Baby Sculpture
The Robinsons' baby sculpture is a prominent symbol of the strangeness of other people's lives, and how, no matter how intently she spies, Harriet will never fully be able to understand why her subjects live the way they do. This is a physical representation of what Ole Golly always says: that there are as many ways to live as there are people on this earth.
