It turns out that the answer, according to this Twitter exchange between a player of Skullgirls Encore and developer Lab Zero Games, is that people who see the above screen have probably not paid for the game.
“So I got this message after beating story with both Para and Cere and I have no idea what it means…”
“Oh that? It means you should probably buy the game instead of pirate it. o:)”
Bravo, Lab Zero.