The United States is very proud of its flag. You see the stars and stripes hanging far more often in the States than you do in most other nations, and it is a very common symbol of national pride. It's hard to go down a major thoroughfare without encountering at least three. While in most places you would only see flags flying over government buildings and similar, here you see them over all manner of residence, on businesses, and even on vehicles.
Major businesses frequently have flags flying before their storefronts as a matter of course. This is a good way to show unity and solidarity to those that visit or pass by, and it is generally considered good form for companies founded in America that are symbols of American enterprise. Always, these flags are flown above the state flag and any flag the business itself might want to display. While this is common practice with large businesses, there is no reason that a smaller business cannot emulate this to the same effect, and convey the same message.
Finding flags suitable for flying out of doors is simply a matter of knowing what brand to look for. Annin flags are the national standard, originating out of American schools. You can find Annin flags at FlagStoreUSA.com and similar outlets, generally at a reasonable price. This makes it easy for any small business that wants to show solidarity and pride in their country to get a sturdy flag that can withstand the sun.