Has anyone else ever spotted this on the streets of this far city?

Only, I have showed the image above to many London historians, guides and friends and, despite the letters shown, which sit on a half inch metal rod, only a couple of people have ever worked out what it means and therefore where it might be. And everyone says something like
"oh, my god, how have i never noticed that myself?!"
Here's a wider view. It's street-facing, in front of a very well-known historic establishment:
Have you got it yet?
It's Ye Old Cheshire Cheese, 145 Fleet Street, EC4. See it on a reprospective Google Streetview here.