The symbol of the tiger is a very important one in How Much of These Hills Is Gold by C. Pam Zhang. It's certainly no accident that tigers appear on the book's original front cover. Interpretations differ, but one could reasonably argue that tigers represent the Chinese heritage that Lucy and Sam's father, Ba, left behind when he came to the United States during the Gold Rush.
Though Ba's children, Lucy and Sam, are Chinese Americans, they haven't completely lost touch with that heritage. It follows them around wherever they go and is represented by the tiger tracks they see in the ground. Tigers aren't native to the United States, and so these tiger tracks constitute a fantastical element to the story; they are not meant to be taken literally.
The tiger tracks can be seen as a physical manifestation of Lucy and Sam's Chinese heritage. They provide a possible answer to the question "Where is my real home?" Lucy and Sam, like their late father, have been subject to racial discrimination on the grounds of their ethnicity. They may be Americans, but America doesn't feel like a place in which they can ever truly belong.
This crisis of identity, brought about by the bigotry of the white man, forces Lucy and Sam to wonder where their real home truly is. The presence of tigers and their tracks acts as a constant reminder that even if they will never be fully accepted in American society, they can always keep in touch with the spiritual ancestry that manifests itself as a living presence within their souls.