A kill order could be signed to punish criminals who consistently broke the Unwritten Rules. They generally only applied to people who even other villains agreed needed to be dealt with.
Signing a kill order involved the local PRT discussing the situation with civilian government, police, judges, and often neighbouring PRT Directors. It involves an "abbreviated trial" and sentencing. While kill orders usually take a while to be implemented, sometimes the process is expedited.
Some kill orders can be pre-signed and used as a deterrent measure. This was the case with Blasto.
↑ 1.01.11.21.31.4Keep in mind that the PRT is in large part a PR organization. They want to recruit wherever possible, and the more kill orders you sign off on, the less people are going to be willing to play ball with you.
As a general rule, the only villains who justify a kill order are those where, if you were to poll the local villain community, Arson Jones is going to say, "Yeahhhhh, you need to put that motherfucker down." Just as a rule of thumb.
In a healthy, functioning city (Brockton Bay is not this) it's not something that's going to come up with any frequency.
What is it? A Kill Order is basically kicked off by the PRT reaching out to other authorities (police, government) and outlining the situation, often through meetings, and often with other Directors from nearby cities getting involved. Given what the Kill Order is, in most cases the police & government already know what's up, and oftentimes there will be discussions that sort of table the kill order until there's one more strike, so to speak.
Once it's made, it's open season. Civilians (and capes) can put money into a reward pool, and it's essentially open season on the target, and anyone who's got permission and knows the general rules (no collateral damage) is allowed to go after them.
Example: Lullaby has been going around and murdering little kids in Bismarck, North Dakota, displaying the bodies in prominent locations. Bismarck doesn't have a PRT office (well, it does, but it's literally a one-room office), so the heroes arrive from St. Paul-Minneapolis, and protectorate members from other cities are called in for backup. There's little need for the PRT to reach out to police and local politicians/senators, because the phone is basically ringing off the hook. A meeting is called in, directors from the various offices around St.Paul-Minneapolis are brought in, as are local politicians, police, and judges. They basically hold an abbreviated trial complete with sentencing. If there's any doubt at all, then it can't go forward.
The kill order is signed (Lullaby is shown on security cameras killing the kids with her signature power, then hanging them up over an alleyway) and the notice goes out. Media is contacted, and local capes make a point of spreading the word in any communities.
What generally happens is that the crazies come out of the woodwork. Intense vigilantes, mercenaries, and villains who want an excuse to get some legitimized violence going on. The heroes switch jobs (and may switch out) to a more management style. Keeping the kooks in line, keeping the vigilantes and the like from killing each other, and providing/gathering information.
Lullaby gets offed by Brazen Bull, a murderer himself, manager of a roaming villain biker gang, and Brazen Bull strides into the PRT office. He collects his reward (about 90% of the $130,000 pot - the other 10% goes to the person who provided the info that helped Brazen Bull find Lullaby) and walks out without being arrested. - Comment by Wildbow on reddit
↑ 2.02.12.2"I- before I knew it, the Slaughterhouse Nine had found me. Shatterbird recruited me. And now I'm stuck. I'm trapped. You know there's a kill order out on me? If I try to quit, either the Nine or the cops will off me. So I keep going, I work for them, and it all just gets worse."
"Surrender? Go to the birdcage?" - Interlude 11c (Anniversary Bonus)
I could make out Miss Militia shaking her head. "I'll be blunt, Skitter. I'm not Armsmaster. I don't have a stake in personal glory or renown. I'm not going to pussyfoot around, either. Put a bullet in her skull and be done with it. There's a kill order on them, nobody's going to charge you for murder." - Snare 13.7
↑ 4.04.14.2A kill order. It was what they had in place for the Slaughterhouse Nine. No holds barred, official heroes would be allowed to shoot us on sight. Any villain or vigilante that came after us would be allowed to go free with only a brief questioning for the paperwork after killing one of us. To top it off, anyone would be able to donate or post amounts for our heads; amounts would be added to running totals. We'd be waiting jackpots for any bounty hunter or assassin looking for a big score. - Queen 18.5
↑To be clear, the self-reproducing creations thing is what gets you labeled as a Class-S threat. That's basically a kill order, but more in the line of "We're going to call in everyone we can to put you down." - Wildbow on MythWeavers
↑With your power, we have an easy way to keep any enemy we capture from wanting to enter the city, and so long as we let them go, rather than using them, we're not drawing enough heat to get a kill order put on our heads. - Imago 21.3
↑"Given precedent, the stakes and the dangers posed by villains unwilling to follow the written and unwritten rules of the cape community, I'd be willing to argue and testify for a kill order." - Queen 18.5
↑Deliberately attempting to divide our ranks could be seen as a violation of the truce, and I will push for the kill order if it goes that far. - Scourge 19.4
↑The Kill Order was signed in record time.
Some of the people taking on the kill order are vigilantes, some are villains relishing the chance to hurt people and get paid for it, and some fit into other categories. The PRT is also in town, more to run damage control than anything else. There are little to no rules, and nothing that the hunters do here will get them prosecuted. It’s a situation that screams ‘opportunity’. - Weaverdice: