> a bus turned upside down is perceived as a plowshare

If I'm thinking of the same picture you are, it's a schoolbus on its side on a snowy road that is misidentified as a snowplow.

FWIW, that picture does look a lot like a snowplow to my eye. Big yellow rectangle against road cleared of snow? If I glanced at it, I might have said it's a snowplow.