Here's my theory: it's going to be a summation of all games shown at the upcoming show. The ice serves as Blizzard in its entirety. The rune shown on the left comes from the upcoming World of Warcraft expansion, Wrath of the Litch King (
source). The second rune, shown to the right, is identical to the Hel rune used in Diablo2 (
source).
My original take was that the splash dealt with Diablo 3 only, hinting to the resurraction of Baal (final boss in D2 expansion, Lord of Destruction). He favored ice, so it was safe to assume Diablo 3 might have something to do with his return.
Now I'm thinking this is just a splash to tease all the games scheduled to make an appearance. I was going to write a news article based on this stuff, but Rob felt that I was "reaching" so here we are on the forum
UPDATE: Rune #3 seen in the south corner is the Protoss symbol from Starcraft II (
source)