imoga-pride:

Gender Unspecificity: different from eligender (othergender) in the sense that it does not state nor specify your gender identity. 

Commonly used as third-gender/aliagender, abinary/nonbinary, equary/nullary & gender diverse/variant item in some documents & formularies after male/female options.

In my case, I have gender identification not specified in my passport because there were no other alternative for it. Reminder there are intersex/trans binaries using it too.

I thought in using the question mark from gender questioning symbol and the currency sign but other-gender one seemed proper. 

-ap