This spanish web affirms that zenimax made a registration of the name heart fire (TES's month denomination) as a trademark. What you think could be this?

(this web also affirms that is a spell book which I guess is incorrect )

http://www.meristation.com/es/playstation-3/noticias/zenimax-registra-la-marca-hearth-fire-nombre-de-un-libro-de-hechizos-de-skyrim/1780220

Maybe Heartfire is TES Christmas?

Really hard to say what it is so i just hope it's something interesting and i wonder if it have something to do with the month heartfire ! can be far fetched but still.

Hearthfire / Heart Fire is September, So i'm just gonna say that's when TES:O comes out? I don't know.

Edit : Oh, and for the book part, they could be just referring to those books named after a date
something to do with the Last year of the First Era, each book has one of the month's I believe.

Hearth fire is also a 2090 book.If you have read any of the other volumes from 2090 you'll find that much of it takes place in Morrowind. In Skyrim you can see that the developers included Red Mountain, maybe there's a connection?