Hints of games

Skins
The first hint was in the Winter skin, where right next to the Snow Drift Yeti is the snowman from Frost Bite 2. This might not be an actual hint, though.

The first skin to actually hint a game was the Horror skin. There are four tombstones. One says "DV 2009?", DV standing for Dirk Valentine, meaning that it would receive a sequel in 2009 (which was not true). The second says "FN 0RP", FN standing for Final Ninja, and 0RP standing for Final Ninja 0.