Safe Zones
There isn't much to say about Safe Zones apart from the fact that they are usually major cities in which Item Shops are available and law enforcement forces. On the map, they are the images framed in green. In the subforums, they have been stickied.
Battle
Indeed, PvP battle will attract NPC guards that may intervene.
It is against most city rules to fight in its streets. As such, should a fight between to OC's reach 3 posts per parties involved, 1 city guard for each party involved will be summoned to put a stop to it.
By then, OC's will have the choice to
1) Let them know that it is a spar and no killing will occur. There will be 1 post attribute to this and though no fighting is involved, it will not be considered a non-combat post so recovery will not happen. This will make the guards allow the fight to continue, but they will stay to make good on your promise. Should you go back on your word, all the guards will then attack you, resulting in a 2vs1 fight.
2) Keep on fighting while dealing with the guards. This would imply that every turn, your OC will be attacked by the other OC and one of the guards, letting it turn into a 2vs1 fight. Only possible if all parties agree on it.
3)Kill the guards off before resuming your fight. This will allow you some reprieve from NPC for 5 posts each before Soldiers are involved and you are placed on a Wanted list, turning the city into a Unsafe Zone for your character.
4)Auto-run to Escape and resume the fight elsewhere, out of the city.
Keep in mind that for every Soldier and Guard defeated, you do get the usual EXP, Coin and Item reward.
Challenging the Authorities
The city's ruler and its soldiers can be challenged without rolling any dice. They are much wealthier than their populace, but much stronger as well. Keep in mind that though defeating them may be bring you good loot, it comes with its own share of trouble.
Victory over City Guard, Soldier or Mayor:
-Obtain the status of Wanted Criminal. The city is no longer a Safe-Zone. Every post would then require a roll that includes Soldier, Humanoid NPC and Ruler. In effect until one defeats a Crime Lord.
-Bounty placed on your head after defeating the Mayor or defeating 4 Guards and/or Soldier. Every 15 posts will have an NPC Bounty Hunter([H][E-Offensive]) trying to attack you. In effect until 5 of them have been killed.
Defeat: Knocked Out
-Jailed for 4 posts where one cannot gain any EXP/Coins. Each post is 150 words long. Lost 50% of one's coins and 1 Lower Tier Item if in possession of any.