(I can’t find the OP on this, so if someone wants to help me out and post it, I’d appreciate it.)
Anyway, while walking in downtown Washington last Friday, I found the Toynbee/Kubrick plaque in the street. It’s at the intersection of 14th and F.
If you’re on the south side of F, walking west (toward the White House), you’ll see it as you cross 14th. It’s a bit faded, but it’s definitely what we were talking about.