An additional note, I have found (non-scientifically) that attitude contributes greatly to "invisibility" If I believe that I am invisible, then I AM invisible, to about 75% of the people who are within eyesight of me.
Eye contact is a strange but true phenomenon, IMHO. If you are watching someone, they can generally feel it even though they can't see you. If someone is watching you, you can feel it even though you can't see them. If you are concealed and you lock eyes with someone else, they will see you then.
That's been my experience.