The Graffiti Express (@thegraffitiexpress@mstdn.social)

I only know so much...but often the tags are an artist's or a consortium of artist's mark/name. They often work in groups and that is why there are sometimes smaller tags - sort of like credits for who contributed. In this example there are a number of people credited in the small text on the left. The tagging often happens while the trains are parked for a while. Grain cars like this one will get tagged while parked in Saskatchewan or in the rail yards of Vancouver.