Hey Dan, funny you brought this one up. I was doing some research as well, trying to look into the architecture of the old Kobukan dojo (pretty hard to find any info on that), anyway, as I was looking for photographs, I stumbled on this one
and was caught by the spiraling up snake/dragon calligraphy in the back. I knew this photograph from at least two books (the one I flipped through today was the bio by Kisshomaru, A Life in Aikido p. 146) in which the calligraphy doesn't show. Here's
an example. In the book it even shows the ridges of what appears to be some piece of white paper or maybe even as simple as tape (cutting of a tiny piece of Ueshiba's skull - if you look close enough).
Significant? I don't know. John Stevens suggested (with a questionmark added) that it might be brushed by Onisaburo Deguchi (Invincible Warrior p.108). Beyond that, I shan't speculate. Just something that caught my eye yesterday.