crewl1 (just realized how that sounds when you say it out loud after all this time! ) and
FantasticMrFox have shown two great examples of differing street or travel photograhy.
So, it is up to you to decide which style favors you the most. crewl1 shows a casual click without being obtrusive viewpoint and FantasticMrFox has engaged at least the eyes of his subjects, if not their minds and hearts. Both are interesting approaches.
While I agree that tourists, travelers and foreigners are not often discouraged, dissuaded, or even disrupted in casual street photography without explicit permission, I personally like the engagement of even a non-verbal permission or acknowledgement. These are human beings, after all. I know there are differing opinions and approaches than mine and they're all of value in differing ways.
One thing I didn't see raised was the age or appearance and "feeling" imparted by the photographer. A slow-moving little old lady with a camera will be received differently than a young athletic aggressive appearing photographer. We cannot change who we are (large person, small person, etc), but we can change to non-flashy dress, casual, relaxed deportment, and engaging attitude. People sense when you see them as "different" or "subjects" rather than "friends."
Blend in and try to feel at home. Then your photography will reflect that back at you. Or at least that's been my approach.
Not all of the objections to being photographed are cultural. Sometimes, the people don't want their picture taken because they're vaguely criminal, or there are political, tribal, or other factors at play. People may be where they're not supposed to be, etc. So....
I guess the word I'm hunting for is "
awareness". Know and understand the situations and circumstances under which you are photographing people. Learn as much about the particulars as your destinations as possible, and work closely with locals or guides to help you understand what people are feeling and thinking.
Anyway, I'm rambling, but you did ask...