Yes, this is a real safety sign. What glorious procedure can simultaneously rip off a chunk of your face, arm, and leg? Lathe whipping.
Here's a 44-second video of some long stock being machined in a lathe. This is clearly done in a modern, clean commercial shop, with a purpose-built support, but it still looks shady. What are they missing here? A second support?
Here's a formal writeup of a lathe whipping fatality from Washington's Fatality Assessment and Control Evaluation program: Machinist Dies After Being Struck by Rotating Steel Bar Stock in Lathe in Washington State.
Worker accidentally pulled into lathe
Lathe safety/stupidity accident video