Reference
librarians are very accommodating, but I don't think I
could ask the Penn reference librarian to go there and take a
snapshot of it for me. (Although you never know, and I admit that I
haven't actually tried).
However, there is no reason why someone who's already there couldn't
take a picture and upload it, and use that as the source. (I don't
know what the copyright is on walls, but it should be fair use if it
isn't free)
It's copyrightable. How long has the text been there? Copyright may
have expired.
Ec