Anybody know the story behind this?

At auction this past Sunday, I bought a scrapbook filled with postcards and a handful of other ephemera, among which was this decal:

The rest of the items in that section of the scrapbook were dated from 1948 to 1955, so there's a probable time frame for this piece, here, but I can't seem to find anything on "2-Spooks Selling Gas" or any variant on it, anywhere in google or the other search engines, so far.

If anybody knows somebody who has either a really good memory of Rapid City, S.D., or access to some historical archives and records, I'd love to know the story behind the naming of this business. Is it a ghost story, a pair of old, retired spies from the war days, or something extremely politically incorrect? What?

I'm all ears.

Well, actually, I'm all boobs and butt, but that's not important right now...