Either he means everywhere or maybe just on letters.
Not a bad idea, Letter from Blarg Tlarg (G) <--- insert gender symbol here.
Uhg, I must protest. That would be jarring. What sort of noble puts his gender in the letterhead? o.o
The title in the signature is usually pretty helpful in determining gender (Knight/Dame, Count/Countess, etc). The unaligned (Noble), and previously-landed (Lord) could use disambiguating, though.