Boundaries:

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Most people  don't have to post a sign...
In order to have people understand what they can and can't do
you must be clear with your signals.
You step forward or backwards as someone approaches you.
Reading signals is an interesting subject and much can be found on the internet.
Check out some of this information and add it to your list
of things you observe when you are out "people watching!"
I don't mean stalking...just having fun with others at the mall while you are shopping!!