The discrete product of a discreet permutation then?
The Wikipedia article says that it was meant to serve the same purpose as end boxes in magazines, and I think it is kind of creative to repurpose that same typographical element for math proofs.
In French, we use the expression: "Sortie de route" (going off the road) when someone says something awkward or terribly wrong. Basically, the real meaning of this expression is that you lost the control of your car and went off road. We also say "partir dans le décor" (to go into the scenery), which is used in the same context. And usually you loose control when you take a curve to fast. Hence this symbol.
In English you can go off the road in a metaphorical way too