O.K...time for a serious post...(if I am going to be an A-hole for laughs, then I'd better get the thread on track when I am done! :asian: )
I am no ninja, but I practice Recon and "invisability" stuff (not sure what you'd call it). I have had conversations with a Native American (Ojibway) on some of the hunting techniques that came from his culture. My Recon and Ranger buddies have shown me tracking, anti-tracking, and some stalking skills. I have read the Stephen K Hayes and Tom Brown Jr. books just for learning purposes.
What I have found from my limited exposure is that if your in the wilderness, your body has a natural ability to blend, hide, and stalk, if you let it. We are animals as well as human beings, so this should make sense. The key is tapping into that natural ability, which is hard to do because we are so far removed from our instinctual selves. I find the best way to tap into that ability is simply trial and error, and practice. You may have good tips from ninjitsu, hunters, trackers, military recon guys, or whoever...but if you don't get out there and play, then you won't hone your abilities.
My favorite way to practice is to track and hunt deer. I don't shoot em' usually; I just try to get as close as I can before they notice me. It's fun, medatative, and a good way to practice your "invisability." I say that if you like to hunt, make it challanging if you want to practice. Don't just sit up in a shelter drinking beer with your rifle and high powered scope. Actually try to track them, and use something that requires a little more skill, and ability to get close, like a bow.
Now, if your in an urban environment, then naturally, your not going to be all cammoed up in your "ninja" costume. There are tactics that you'd use to blend and look like anyone else. I'd imagine that you'd want no one to notice you; but if they did, they wouldn't think about it, and they wouldn't be able to describe you. I am less versed in this aspect of "invisability."
I'll bet that some of the tactics from Ninjitsu work as well today as they would have hundreds of years ago. I'll also bet that systema has some good modern insights to this sort of invisability.
Now...time to go run around in the woods nekid.
Your friend,
The streaker
p.s. lets talk about urban invisability, beyond the obvious of "don't look noticable." Any specific tactics you'd like to share?