... and in fact it can be even more subtle than that. I have some genderflexy characters who don't switch pronouns, or don't always switch. They may or may not explicitly describe themselves as genderfluid, queer, whatever. You can just write them as they are, and some readers will clock them and others won't.

For examples, see Quinn in Schrodinger's Heroes and Maryam Smith in The Steamsmith. You might also like "Crosswise," a poem about Quinn switching between masculine and feminine modes explicitly -- but without ever revealing the precise sex of the body.