To be clear: whatever the button is called, it doesn't have any text on iOS (which, as far as I can tell, is what OP was talking about). It's just an icon of a pencil writing on paper.
To be even clearer: It's literally one of only 4 buttons on the main Mail screen (the others being Back, Edit, and Filter). If you just go to Mail and don't even attempt a guess, that's on you.