Well, yesterday, as Jedi Consular I went rampage in the Sith Ilum camp, murdering many NPC's under the waking eye of Sith players. Made it to the cantina, Battle of Ilum/False Emperor (I think? Not sure if same on Emp side) flashpoints and roamed about the upper level with the vendors...
No PvP flag.
So... that doesn't quite match with what people said before about the flagging system... :/