This is a very simple protocol to prevent friendly scripts from annoying residents.

Listen on port 666 for the message "PowerWordKill" (notice the capitalization). Whenever your script hears this message, llDie().

Why? The more this convention becomes standardized, the less potential for accidentally annoying scripts. For example if most residents know this protocol, and a legitimate self-replicating script grows out of control, they can shout PowerWordKill.