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?
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
Yes i think it is correct thankyou for the great information
20 minutes well spent:
https://www.youtube.com/watch?v=5K8UpMNYIPo