20 minutes well spent:
https://www.youtube.com/watch?v=5K8UpMNYIPo
Yes i think it is correct thankyou for the great information
If this is what you saw, it's KarTrak. It was a system to keep track of the car - same technology as the bar code on stuff you buy at the grocery store.
https://en.wikipedia.org/wiki/KarTrak
Some cars that i saw had a welded plaque on the side near the car end ladder looks like it had coloured lines on it. Maybe lines for load height limits?