I'm guessing it's short for "If you don't know what this is and you find it outside of any shielded box, shit has gone very wrong and you should not be near this, let alone touch it". The probably best way to get people to stop touching it is to suggest that it poses an acute threat, hence the urgency in the phrasing "drop and run".

So if you're operating a device wherein it's properly contained, you don't see the label. If you're removing it while protected appropriately, you already know the label doesn't apply to you. If you know how to handle it, you don't need instructions.