A type of graffiti-writing style present in San Francisco; namely, the San Francisco public transportation system. It is the act of tagging with a particular style on a San Francisco Muni
Bus that blends with the pulse of the bus ride. It's not called Bus Flow for no reason; you gotta have rhythm. Takes a lot of practice and hard work to master. Very illegal as graffiti is a form of vandalism.
Graffiti takes dedication and hard work; some people takes years to even realize what Bus Flow is.