A quick regex search of the available berklist archives show it to be in use as early as January 1995, and most probably earlier, since it was used without explanations as to its meaning.
It means:
"I'm toiling away for my overlord so I don't have my books handy and I'm pulling this from my inadiquate memory. Please refrain from flameing me if I'm incorrect."
The Ars 'community' is pretty tight, but it's also likely very small and it's interesting to me that it's developed catch phrases that out side this nuanced group have no real world meaning.
I hate to have one two many beers at the bar and while talking politics with some stranger say, "Serf's Parma but...."