Those flags are Tibetan Prayer flags...I have a set of them flying in my yard. The set I bring with me backpacking and camping were brought back from Leh, India, by a friend of mine. I began flying them many years ago when my brother-in-law was sent to Iraq and have continued flying them for all of us.
Here is the story behind the flags:
http://www.tibetanprayerwheels.com/prayer-flags.html
This is not where I'd buy them but it does have a good explanation as to their meaning.
See them flying over a campsite and you might very well find me nearby...it has become something for which I am well known with my fellow backpackers...
I think my favorite picture of the flags was this one taken at Devil's Tower from inside my tent:
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