A comics artist once told me the pros often throw stuff like that into backgrounds, because it adds another layer of enjoyment to readers,
who can go back and look at the art later and enjoy details like that on re-reading, even after they've already read the story.
I don't think Calvin and Hobbs existed in 1980 when that cover was done, but the kid with his doll is reminiscent of the character, and it would
be a nice tribute cover to see!
