Joe A. and YardRat, thank you, great info!
It seems that in the old videos and photos of full out trains there are no cards on the boards. Maybe I just never really look quite close enough. Would the cards usually get removed before the train hit the main line?
YardRat, you said "inspected at a certain date by a particular inspector. These marks were at the ends of the cars and had a cross through them", so initials and date would be a prototypical thing to scribble? Also, sorry for being dense, but can you elaborate on "a cross through them". Do you mean that one guy would inspect and write it, then someone else downstream would check it off by crossing through it? Or is that at next inspection the guy putting his initials and date would cross off the previous marking?
Finally, why do I care so much about these things? You guys understand that as well I am sure. 
