Reverie has made a fancy spray with the Deadly Pandas logo, for you all to download and use! Get it HERE. If it doesn't prompt you to save, right click the link and Save Target As. Go to Options->Multiplayer Tab->Import Spray, and select the TGA file you just saved.

You can use this with just about any Source-based game, like Team Fortress 2, Counter-Strike: Source, etc.

Happy gaming!