We can surmise (with accuracy) that the persona of the speaker in Maya Angelou's "Still I Rise" is female by studying some of the images the author presents as well as the diction (word choice).
In the poem's second stanza, the speaker uses the word "sassiness." This is a word historically used for small children and women:
Does my sassiness upset you? (5)
The image presented here is that of a black woman standing up to a white society—this is why the speaker says "upset you," for should a white woman speak up for herself, it would not generally be an occurrence that would create uneasiness in its audience.
In the fourth stanza, the description used is one also long associated with women, especially in patriarchal societies:
Bowed head and lowered eyes... (17)
(Arguable, this is also a signal of anyone being oppressed: lowered head and eyes describe the behavior of someone before a person of great power, e.g., a monarch or a slave owner, or anyone white).
"Haughtiness" (in line 17) is often associated with a woman. Lines 17-18 give a description that is more feminine than masculine in nature:
Shoulders falling down like teardrops,
Weakened by my soulful cries?
"Shoulders falling," "teardrops," "weakened," and "soulful cries" are likely more apt to bring a woman to mind as they are characteristics often associated with women.
Perhaps the lines that are most obviously feminine are those that provide sexual imagery regarding the female body:
That I dance like I’ve got diamonds
At the meeting of my thighs? (27-28)
While Angelou's poem speaks to the oppression of all people of color, it is the persona of a woman that is present in the poem.