http://www.psfk.com/2010/04/chalk-mented-reality-city-guide.html
Basically, there is a zine of sorts in London and Scotland that is for the homeless. It created a sort of code that the homeless could use to designate where is a safe or unsafe place to stay, whether there is food, etc. I think this is a revolutionary idea to help the homeless and make it that much easier on them. Plus, the fact that there is a magazine for the homeless is a good idea.
also, I stumbled on this page
http://blog.makezine.com/archive/2009/03/bike_accessory_leaves_a_trail_of_ch.html
In both cases there is a definite and large community, but they do not always congregate together. Chalk is used for communication when physical communication is not possible. For the homeless, it is used to relate important messages while for the bikers, it is used to give a sense of the others in the community. I think it is important to do this because, especially for the bikers, that there are others biking instead of driving. This provides a sense of belonging and maybe even encouragement to keep biking.
