Utilize common sense... For every 100 or more freight cars there is ONE, maybe two engines which are maintained and inspected DAILY. Given that information you should be able to piece together that in painting an engine it allows the workers and rail security to know that THEIR yard is being painted. It goes for numbers as well. Workers fucking hate not being able to have the information they need to get their job done, and rightfully so. To write graffiti you have to be aware and conscious of your surroundings and what your actions are effecting. At least to sustain a somewhat lengthy period of time of actually getting it. A lot of it is about trial and error, but I'm trying to throw in my tid bit so spots stop getting blown up by petty kids painting petty shit like twice a month. A lot of people want to be graffiti writers, but most are too scared to do it proper... Or lack common sense and knowledge. Good day to you lames