How does Orwell's use of symbols in the novel reveal themes in 1984?
Most of the symbols represent the freedom of thought and choice to do what one wants when one wants--for example, the diary Winston purchases and writes in just out of the view of the telescreen, and then hides each time he leaves the apartment. In it, he writes about how he hates Big Brother (another symbol--since he is not a true person...just a figure head of the society).
"The Bells of St. Clements" and the paperweight Winston purchases in the black market are also symbols of this freedom...a time in the past when people could do nothing or everything as they chose to. Of course, the paperweight also symbolizes the love affair Winston has with Julia--it's transparent, beautiful, and fragile just like their relationship. The coral center represents their love, but since it is easily seen, it also represents the fact that they have been observed the entire time of their trist even if they didn't realize it entirely.
The Prole Woman and her song is also a symbol of freedom and a time that has been which Winston hopes will come again.
There is also the Chestnut Tree Cafe. A place that Winston sees as an area to exchange ideas, but turns out to be more of a "holding cell" for the doomed. The three conspirators drink and eat there until they finally disappear forever, and this is where Winston basically lives at the end of the book.
Perhaps the biggest symbol that is seen throughout the novel is the face of Big Brother. Big Brother is powerful and is seen everywhere. Winston often confides that he feels the eyes of Big Brother following him, which is not unlikely that he would feel this way since the posters of Big Brother run a caption that reads "Big Brother is watching you!". The power of Big Brother is actually a theme in this book. The Party, with the use of Big Brother, has a powerful hold on its people. The government has total and complete control right down to thoughts its society thinks and the language which they speak.
The paperweight and journal which Winston purchases are symbols of his betrayal against the party. In possessing these items he has committed several crimes, the worst of which is thoughtcrime.The Party demands absolute loyalty and go through several measures from a child's birth to ensure that the only loyalty existent in a person's life is to that of Big Brother. Winston possessing these items which were pre-revolution demonstrates his disloyalty and betrayal of the Party and Big Brother.
There are several other themes that are revealed throughout the novel, but these had the clearest symbols to represent them. See the link below for a list an explanation of themes from eNotes.