We got the news from WoWinsider that World of Warcraft: Wrath of the Lich King will include inscription, they takt a first look of the inscription in patch 2.4.

Blizzard has included the first look at inscriptions via hidden entries in the patch 2.4 data files. Inscription will be a new profession that will be released with Wrath of the Lich King. We are treated to an early glimpse at the Demonic Runes inscription that will increase fire damage done by the Mage Fireball spell by 50 additional points. The data is courtesy of WoW Head.

There are two important things to realize from this newly discovered information. First, it shows that Blizzard is hard at work on Wrath of the Lich King, and is already starting to include content in the patch files. We saw this same behavior in patch 2.0 with Jewelcrafting recipes.
Gallery: Wrath of the Lich King

Secondly, note the rank of the inscription. Rank 3. This is a strong indicator that there will be multiple ranks of inscriptions and power increases. If Blizzard holds true to current formulas and mechanics, we can expect a mostly linear trend in the amount of power granted by the inscription.