Either
in reply to a message by BBH
If it's somewhere I'd expect to see a formal name, like the arrest blotter or a class roster, I like to assume it's a male. In more casual contexts I just can't say. I think Jan is a terribly handsome name for a boy and pretty meh for a girl.
I used to work with a man called Janis. Customers who called for Janis did not generally interpret his name correctly.
I used to work with a man called Janis. Customers who called for Janis did not generally interpret his name correctly.