They took a picture of the display.
That picture was what I held in my hands: The very first photograph taken anywhere in the world using a FLIR system.
Two weeks ago, my father passed away. While going through his things, I came across the picture and figured folks here might be interested in a bit of history.

I also spent some time on google maps trying to figure out exactly where the photo was taken. It wasn't easy given that the photo would have been taken nearly 50 years ago and much has changed, but I believe I have found the location. Note that the FLIR would have been facing west.