On Fri, 29 Mar 2013 18:54:31 -0800 Floyd L. Davidson wrote:

It is private property that is open to the public.

That means you can photograph to your heart's content as
long as the manager or clerks do not object. They do
have the option to ask you to leave if you don't stop.
Not leaving would put you in violation of tresspass
laws.

Do you know where we can find this written down so that
I can show it to the postal service?

Here, for example, is a sample pic (with identities blurred):
http://www2.picturepush.com/photo/a/...g/12561500.jpg