The ghost sign originally read "Reid’s Crystal Hall Crockery, China, Glassware, Wholesale and Retail." In the meantime a mural has been painted over the sign... with a catch. The artists decided to take the steps to protect the ghost sign. The team of artist used a clear spray paint, typically used as a top coat, to cover the sign. They covered it with the graffiti proof coating and painted over top of it, so in time, after the mural fades, you can literally just wash it off and the ghost sign will be visible. You can view the mural here. I'm linking to Lesley's Signs, Signs.
Why preserve them?
1. Every one of these signs was hand-painted. When you see how sharp and neat some of them are, it’s amazing what they did by hand and not by stencil.
2. They identify who the building was, who used it, and who was there.
3. It shows you the age of some of these buildings.