Wow, you guys are harsh! To me, a person is following etiquette if their first step in this process is to simply communicate. You don't know anyone's intentions if you don't find out, and vice versa. You might find someone who is hunting a different species, scouting for a future season, or doesn't hunt like you do....none of which you would know without communicating.
My unwritten rules: if I were to see a hunter shoot an animal, I offer to help track, process, and pack. If a hunter were to cross my camp or me during meal time, I offer them one. If I run across anyone, a wave, smile, and conversation are the norm. I also always ask of they need anything; TP, water, etc.