What does the golden giant in a 'Tale of Two Cities' represent?

I think you mean golden "thread." The golden thread symbolizes a few things: Lucie's golden hair The thread that ties together the different characters of the book So... Lucie is the "thread" which connects certain characters in the book...

ACTUALLY they do mean the golden arm of the golden giant in book 2. it symbolizes the oppression of the evermonde family on dr manette