It seems to be the week of trademark applications. ZeniMax Media has followed up its recent patent for Dragonborn and the "Fus Ro Dah" shout with another tasty trinket.
This appears to be a reference to the skill book "2920, vol 09 – Hearth Fire" in The Elder Scrolls V: Skyrim.
Skills books provide players with special rewards. Hearth Fire is part of a 12-piece collection that gives players the chance to summon creatures from the dead or create weapons from the energy of souls.
The trademark was filed on 24th May, but Bethesda hasn't made an official announcement. More DLC on the way?