Which Clues Immediately Tell the reader that he or she is reading both an autobiography and the story of a person who had been enslaved

The second paragraph of chapter 1 makes this clear:

The reader will pardon so much about the place of my birth, on the score that it is always a fact of some importance to know where a man is born, if, indeed, it be important to know anything about him. In regard to the time of my birth, I cannot be as definite as I have been respecting the place. Nor, indeed, can I impart much knowledge concerning my parents. Genealogical trees do not flourish among slaves.