Here’s a photo of the original “Metro Warbird” plane, November 4529 Kilo.
(Photo courtesy of Bernie Ockuly).
The story I’ve heard is that the owner of this plane liked to emphasize that, since it’s a Navion, it actually was a warbird, (a plane once used by the military). Hence the “warbird” part of Metro Warbirds. The “metro” part came from the company that used to handle the port-a-potties at Oshkosh. Evidently, someone heard the warbird comment one too many times and slapped on one of the toilet stickers, as sort of an editorial comment.
The name stuck, and twenty-nine years later, we’re still the MWBs.