I am going to back from dead just to say this.
Let’s consider these things:
1-A person won’t know what is yours until you tell them.
2-A person that does not know you won’t care, because looting.
3-A friendly person won’t know what is yours until you tell them, like #1.
4-A system that could work would be to command the NPC to not grab any thing from an area. The map pops up, and you will choose wich areas are your territory. Do this with every NPC that you want to be with.
5-In this case, hostile NPCs can still loot because looting, and friendly ones (that know about your territory) no.
6-This makes defending your base from looters possible and fun.
7-Killing hostile NPCs in your territory should not hit morale that badly.
8-There is no “magical cr**” here. It’s basically how it would work in real life.
This is also, in a vague idea of me, easier than other ideas and also does not need to have a claimed tag for ALL the things, just for the area.
Also, other suggestions:
9-NPCs can and will claim a territory (or at least to have them pre-generated), but it should have the following things (if possible)
-It’s a safeplace, wich means no zombies near it.
-It has got loot. NPC territories could have also a boost for the apparition of items, this including guns and food, survival stuff.
-The NPC could either be kind and do nothing to you, or attack if in the territory.
-Stealing from the territory can be done, but after stealing, if the NPC sees you with one of his items in your inventory, it turns hostile.
-To know about territories from NPCs, you could ask other NPCs or chat to the owner of the territory (and he could tell you about the place)
10-This system can also make having bands of NPCs easier, because they could spawn all allied to each other and all could use the things in the territory. (If possible)
11-Hostile bands could be possible too, like the bandit camps. (if possible)
12-Can NPCs target each other as enemies? I have never seen them do so. If possible, this has to be boosted, making them friendly or hostile, wich could make the game far more interesting. As stated before, friendly NPCs let you be in their territory.
13-Killing the NPC owning the territory deletes it and you can grab everything freely. Same if he dies naturally.
14-If you die, NPCs that you told about your territory can take your stuff freely.
15-NPCs that kill you in your territory will claim it (This could make a lot of fun revenges, huh?)
That other things, even if a lot harder and needing a little too much NPC work, i think could be AWESOME and INMERSION GIVING for the game.