Apologies for resurrecting this thread.
I came across the inscription on Eyewitness works a few weeks ago and decided to make a rubbing of it. Since there is more interest in Eyewitness works at the moment (with the recent Mausoleum of Giants exhibition) and the buildings upcoming conversion into flats I thought people might appreciate it if I shared the outcome of the rubbing (and an enhanced version of it).
In terms of the history of the inscription, I cannot add anything beyond what is discussed in the thread - other then to confirm that my own research hasn't offered any better theory for the inscription origins.
I just hope that when they redevelop the block they don't destroy it - since its been on the building for more then a hundred years!