I had assumed it was a former real estate agent's shop, with some cheeky changes made. But the changes looked as old as the original sign.
A couple of days ago, I was driving past with a friend. He said he knows the guy who owns the building, the former PR guy for the Rainbow Warrior, the Greenpeace boat. He'd hired a signwriter to create the 'Secret' in the same faded style as the rest of the ghost sign.
Nice one, and case officially closed :)