I saw that phrase on someone's post on Facebook. I think it's not appropriate to talk about the detail source (screenshot) in which I found that phrase. To be precise, it says:
My pronouns are he/him
Did he refer to his gender or what? And if I'm not mistakenly remember, I've seen also someone says my pronouns are she and he. I don't understand.
Best Answer
In these days where gender-fluidity is a thing, it is often unclear what specific gender some people identify themselves as. It is often important for emotional and psychological reasons that they are addressed by the pronouns which match their personal identity, and to ensure this is the case, they announce to the world how they prefer to be addressed.
Hence:
tells people that the person identifies as male, and therefore wish to be referred to by male-identification pronouns.
But as for someone who says their pronouns are "she and he", I haven't a clue.