The Mafia-style dirt-covered shovel -- code for digging your own grave -- dumped on Friday at 3.30am on the doorstop of Kathy Jackson, the union official who had the courage to refer Thomson's activities to the police, may as well have been delivered to the Lodge.
Is there any previous instance whatsoever, in fiction or otherwise, of the Mafia using a shovel as a threat? Or of anybody else doing the same? The top 100 entries on google for "shovel, doorstep, mafia" don't happen on an example (other than in the Milne article). "Shovel on doorstep", 2 entries, both recent Australian; :"fish on the doorstep", 17, beginning with The Godfather, and "sleeps with the fishes" lots (despite, apparently, it not being used in those words in The book of the Godfather).
The risk, surely, is that if you're the first person to invent a particular rebus-based threat it may well be misunderstood. Code has to be a recognised convention.