Yes, that was a Mayer thing.
When GuitarWorld asked where the name came from, JM said:
”I don’t remember. I think it might’ve been a broken piece of a song idea. I liked it because it sounded like a secret operation: Project Silver Sky. I sort of imagined a congressional hearing being assembled to find out more about this “clandestine Silver Sky venture.” I also felt it was in keeping with Paul Reed Smith’s bird nomenclature.
In another way, it reminded me of things like the Broadcaster, the Telecaster and the Stratocaster—you get this sort of air and sky vibration from the name.”