I feel like I don't really do much graffiti around my railroad, but there is some here and there. And if I want the setting to be urban and somewhat contemporary, I probably should have a fair bit more than I do.
Here's a boxcar that I weathered up a couple of years ago, inspired by photos on-line and a fistful of graffiti decals that my friend Luc gave me. The boxcar is from the Atlas Trainman line. Although the Trainman line may not have the detail other brands do today, they're not easily damaged either and that can be a positive thing.
I first airbrushed over the boxcar brown with acrylic Terra Cotta to tone it down, then painted in the patches. I put the graffiti decals on and then followed that up with washes of thinned black acrylic top take the shine off everything. Dullcote too. (Edit - Well, actually the Dullcote was done at the very end.)
I found the decal of the Spanish looking gentleman to be particularly interesting, and thinking he'd go well on a car from Mexico, placed him prominently on the boxcar door. The star at the right-hand end of the car is my own artwork with a white paint pen. I was given the vertical Ferromex decals by Sean Steele. The white reporting marks and numbers are from a Microscale alphabet set.
This boxcar make occasional appearances around the JSSX. Special thanks to Luc and Sean.