American Trackless Door Hanger

I came across three of these large metal objects in my attic and wasn't sure what they were. Recently I decided to investigate further and found some markings on them that led me to identify them as American Trackless Door Hangers - check out this video to see them in action (not mine, I found this video on YouTube): https://www.youtube.com/watch?v=UwWNjAKF42I

Anyone have any idea what they might be worth, or what the history of this item is? Seems like a damn cool piece of hardware.

Thanks for any tips or suggestions.