The code has been there since the beginning. If a bigger threat shows up, we band together. We don’t distract each other with attacks or murder attempts, we don’t take advantage of the situation to fuck with civilians. The truce is there for a reason, and it has weight because everyone knows that they can’t handle the trouble that gets express-delivered to their doorsteps when they’ve defied it.
The Unwritten Rules, also known as the code or the truce, were an unofficial code of honour adopted by capes. It existed in multiple countries, including much of North America and Australia, but not Russia or the CUI.
Skitter was accused of breaking the unwritten rules by allegedly taking advantage of the Battle against Leviathan to learn Shadow Stalker's secret identity. As a compromise, it was suggested that she could reveal her identity to Shadow Stalker, for which there was precedent.
Armsmaster was considered to have broken the unwritten rules by steering villains into the path of Leviathan without telling them.
↑ 2.02.12.22.3"You violated the code by association when you took someone, took control of someone. The same someone who you saw unmasked. You violated the code again when you attacked Triumph's family. So what's stopping us from tearing off your mask right now? The same code you've disrespected and broken?" - Queen 18.3
↑ 3.03.1"Taylor," Charlotte whispered. "If they know who you are, they know. They could find you again, or put your face on the news."
"If they did, it would be breaking a good few unwritten rules. Especially if they only knew who I was because I helped with the Echidna situation. They can't afford to punish villains for helping against the big threats. It would mean fewer people showed, and they need all the help they can get. Here, at least, they could say I was intruding on neutral ground." - Chrysalis 20.4
↑ 4.04.14.24.34.44.5Unwritten (well, some are written) rules in the cape community extend to: no murder, no rape, no going after families, you maintain the overall peace (generally meaning keeping the truce and not being such a monster/threat that people can't sleep in their beds at night - Bakuda broke this one). You don't **** with people's secret identities or private lives (ie. their families), etc, etc. Different areas maintain different variations on these rules. Breaking these rules may get you sent to the Birdcage. Consistently breaking them may get a kill order placed on your head. - Wildbow on MythWeavers
↑ 6.06.16.2You've heard about it happening. Someone finds out another cape's secret identity, goes after the cape's family. Or a cape wins a fight and decides his downed opponent isn't in a state to say no if he's feeling lusty? Word gets around, and the cape community goes after the fucker. Protecting the status quo, keeping the game afloat. Bitter enemies call a truce, everyone bands together, favors get called in and everyone does their damndest to put the asshole down. - Excerpt from Agitation 3.6
↑ 7.07.17.2"You know the rules, here?" Grue asked Trickster.
"We've been to similar places. I can guess. No fighting, no powers, no trying to bait others into causing trouble, or everyone else in the room puts aside all other grievances to put you down."
"Close enough. It's important to have neutral ground to meet, have civilized discussion." - Hive 5.1
↑I'd like to keep to the unwritten rules, as abused as they have been, lately. Killing should be a last resort. - Interlude 20
↑ 11.011.111.2"They've broken other unspoken rules," Assault said, looking at Triumph and Miss Militia rather than the junior members. "Shatterbird? Are we really going to let that one slide?" "Anything goes when fighting the Nine," Miss Militia said. "The Nine are gone. He's still breaking the rules. He kidnapped and took control of Shadow Stalker. He's affected civilians. Criminals, admittedly, but still civilians." - Interlude 15
↑ 13.013.1I couldn't really believe they were going to arrest me. Like Tattletale had said, there were rules. Largely unspoken rules, but still more important than anything else in the cape community. You didn't profit from an Endbringer attack, you didn't attack your nemeses or take advantage of undefended areas to steal. You didn't arrest a villain that came to help.
Because when people started doing that, the truce broke and things became ten times easier for the Endbringer. - Extermination 8.6
↑ 14.014.1The code has been there since the beginning. If a bigger threat shows up, we band together. We don’t distract each other with attacks or murder attempts, we don’t take advantage of the situation to fuck with civilians. - Cockroaches 28.5
↑"Tattletale," Miss Militia said, "I'm going to remove the gun. Think very carefully about what you say. 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
↑"You broke the truce when you said what you did about her. You risked breaking the ceasefire between heroes and villains that stands whenever the Endbringers attack."
"I broke the truce before that. I set others up to die." - Interlude 10.5 (Bonus)
↑ 17.017.117.2"But we have a store of equipment we confiscated from Bakuda when we raided her laboratory. Miss Militia deployed a number against Leviathan, but we have more. Once the other factions have engaged, we bombard the area with the remainder in a second strike. Our research suggests that several of these explosives can bypass the Manton effect."
"This breaks the unspoken rules between capes. And the truce against the Nine. I don't like this." - Interlude 13
↑ 18.018.1"It's like I was telling you, Taylor, someone breaks those unspoken rules, the community protects the status quo. Us villains make truce with the local authorities, we actually work together, in a way, with the cops, capes and military holding the line during the day, and taking down any ABB members who stick their heads up, while us villains do the nitty gritty stuff… In this case, it's probably more blatant an invoking of that than any example I can think of. Guess we can thank Coil for that." - Tangle 6.1
↑"It's customary for there to be violent retaliation if someone causes trouble at a meeting like this," Skitter said. "Usually involving every other party that's present." - Interlude 20
↑I could go on a whole spiel about the unwritten rules. But that's not important. For people like Tagg and Piggot, it's cape business, and they're not quite part of that. - Imago 21.2
↑You broke the unwritten rules, because you think that you don't have to obey them, since you aren't a cape. Except you're forgetting why they exist in the first place. The rules keep the game afloat. - Cell 22.3
↑Gavel. Cell block leader. A vigilante who had gone after families, particularly spouses and children, all so he could break his enemies before his namesake weapon could. He'd been notorious in the days before the three strike rule or even the code. - Extinction 27.3
↑Brockton Bay, in large part, was sitting this one out. Hannah wasn’t a true asset against Behemoth. Besides, the truce was in worse shape than it had been even in the beginning, and the portal too important. -  from Interlude 24
↑“My concern…” a woman said, drawing out the thought, “Is that her actions go against the spirit of the PRT and the groups under the PRT’s umbrella. Conspiring with a known terrorist, betraying the truce, even, for a subtle advantage in dealing with that terrorist, returning to her old team against all terms of her probation, rejecting orders, and taking reckless risks with PRT personnel, getting two injured. A longstanding goal of the PRT has been to reassure the public, and this only paints heroes as something dangerous.” -  from Scarab 25.1