This replaces one of the Sniper's Jarate voice clips ("Heads up!"*) with an energetic "God save the piss!"
4 versions are included, they only differ in the intonation of the last word.
How I got this idea? Because of part 5 of my Team Fortress 2 series on YouTube (2:25).
Very odd that I made that "line" long time BEFORE the update... whatever.
Of course that one is the preview you can hear here.