The phrase Cool "Disco" Dan (the quotes are part of the phrase) has been used for various forms of graffiti in the Washington, DC metropolitan area. This mark has generally been used as a form of vandalism in graffiti spray painted onto various areas. It is the work of an individual from the Washington, DC area who has been spraying his tag since 1984. Wikipedia
The definitive Wikipedia entry for Cool "disco" Dan. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Cool_%26quot%3bDisco%26quot%3b_Dan