I don't know that you would -need- to openly announce to the person that you're going to PK them as much as you would need to do some amount of RP with them before giving them the axe. I believe that the primary reason players have been punished for not adhering to rule 1 is that their one and only interaction with the character they killed was PK, and not because the other character was attacking their city or one of their allies or there was some other pressing reason to attack the character.
Here's an example, and I'd appreciate Thuban's perspective as to whether this example is valid.
A necromancer walks into an inn, seeing a mercenary of Alshain. He asks him how he's doing, inquires as to whether they had any family or if they liked the weather. The mercenary talks amicably with him, unaware of the identity of the person he's talking to. As the necromancer turns to go, he says he has one last thing to say... before casting FoD and killing the mercenary, followed by animating his corpse and making his undead skeleton wear his symbol of Alshain while murdering a hapless child. "Death to those deceived by the falsehoods of truth!" he screams before hastily recalling.
I don't think this situation should result in any punishments for the necromancer, because he interacted with the character he PKed. I'm not too convinced that you can "cover yourself" by posting something on the astral board either, honestly: That's at best the absolute minimum requirement and leaves you open to being validly punished.
Rule #1 is meant to serve as a reminder to players that you should remember that other people want to play the game just like you, and you should be willing to alter your RP to accommodate that. Yes, technically if SK were "realistic" then a diabolic necromancer would have no problem with killing everyone they see with no warning, and with NPCs that's a completely valid approach: With regard to PCs, however, there needs to be an extra measure taken to ensure that the other person is getting more RP from you than the kill command.
Quote:
Gear your roleplay to be inclusive of other players. This
means many things, but for example: you need to roleplay before
killing, even if your character is diabolical and insane.
However blurry it might seem to some, there is a definite line between killing people without any interaction at all, and broadcasting your direct intent to murder someone so blatantly that you're guaranteed to put yourself at a disadvantage. The question you should ask yourself is not "Am I sacrificing my chance to win by roleplaying?" but rather "Is it worth ignoring the rules just to get a kill?"