Symbolism

The paperweight is the most obvious.

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The diary is arguably the most significant symbol.

It's provided to Winston by way of the antiques-shop run by a member of the Thought-Police:

The artefacts there are meant to arouse curiosity about the past- a concept normally not accessible to mere mortals, since the past is constantly re-created--

by people like Winston himself.

This way, they ensure that always there "...were fresh dupeswaiting to be seduced by him" (Goldstein).

The diary is not a book containing information about the past, but a means to record one's own past...

Winston thus is trying to record his.

But since he has grown up in a world in which the past is an artificial construct, he can not have any objective understanding of what 'Past' really means:

His perception of the past will always be based on what he himself knows- and how he understands the principle itself.

All of that is shaped by Big Brother.

If he would attempt to write anything about his parents or grand-parents, he would inevitably create his ancestors in his own image.

Which is precisely what the rulers are doing all the time- by constantly re-writing history their own way-- and by translating Shakespeare into 'Newspeak'...