For one, do not go bombing in pitch darkness. I was planning on doing some throwups on a freight car that was parked not that far from me. I lost track of time and when I went to go do it, I literally had no idea where I was painting. I took a quick flash photo as I saw people not that far away from the freight on the other side and left. I saw what kind of junk I've been painting. Going around sunset and sunrise are your best bets in my opinion.
I cannot stress this enough. ^^^ Best advice here. And not just the yard, don't leave anything anywhere. The idea is to get in and get out and leave no trace you were ever there. But yards especially. They see cans, caps, paint on the rocks, they will know it was painted there. Also. If you paint small yards, DO NOT paint more than one car at a time. You paint more than one, they'll notice. They do keep track of these. Also if you post photos of your car you did, before it leaves the yard, blur out the fucking numbers, police track that if the rail workers report it. So they match up the numbers with your flick, and in a time frame it's been sitting in that spot, they got yah. Honestly, being paranoid as all fuck is the best policy with freights.
then you gotta quit the graffiti's or write an apology letter to the person and throw in a blow job or two.