Snowball Fight help??

Since I never remember this every year does anyone know the code to put on a full layout so you get the snowball box that allows other players to hit you?

 I know I've done it in the past but I obviously didn't make a note of it and it was on the forums at least 3 years ago that I read the post that had the code on for said box. 

Any help would be greatly appreciated :) Or if it's not possible now forget I said anything!

[snowballbox]