Here is the picture I was referring to.
The pictures of the Land Mattress are covered in Numerical 82 at the Canadian Archives. (relevant pages attached to this post)
https://recherche-collection-search....&app=FonAndCol
Another series of pictures of the Land Mattress appears in the Imperial War Museum collections online. And I think 3 videos appear online of the Land Mattress in action (one Canadian Newsreel, 2 British IWM), but so far I have only seen the C30 LAAT tractor in the 2 pictures in this thread.
Neil, did you manage to find out more about the markings?