I'm not sure if this is a bug, or if I'm just doing something wrong (or right?). It seems I can find myself no humanoid enemies. I know there are threads about that already, but my specific problem is that I cannot make enemies. I've decided to be hostile towards the legion and powder gangers on my first play through for this game. So, I kill them all on sight a lot of the time. I've killed dozens of legion and powder gangers, and I'm hated by the former and neutral to the latter. Even hated, the legion won't attack me unless I shoot them, and even then (I'm a sneaky sniper), most of the time it's just that one person. The the other hostiles' red marks on my hud turn back to orange after he dies.

Are they not finding me because I usually go right back into hiding after I headshot one of them, and having had no visual ID on me, don't know that it was me? They have sent a pair of assassin's after me who told me I deserved to die, before I killed them, so I was assuming that the rest of them would want me dead too... but that's not happening.

Are you wearing Legion armor?

Do you have the Mark of Caesar?

I'm not wearing their armor, and I didn't get the mark until an hour ago(after I made the OP). I may have put on the armor for 5 seconds to see how it looked (don't remember if I loaded after trying it or not), but I was in the middle of nowhere and there were no legion or NCR in my perception range (9 per).

I've had enemies' markers flicker between red and normal a lot, but it doesn't mean they are going non-hostile.

If you are sniping them from a distance, they may not know it's you. Have you tried walking right up to them and shooting them in the face like a big burly manly man?