When they're pronounced dead at the scene, you know it's bad. That only happens with what the NTSB calls "injuries incompatible with life", which is right up there with "controlled flight into terrain" as one of the NTSBs top morbid euphemisms.

In our EMS system, there are a few situations in which BLS providers (EMTs, without access to an ECG) are allowed to declare someone dead in the field (note, coroner, police, etc., may still be involved, and they're not signing the death notice)...

"Body position incompatible with life" is one.

(For the morbidly curious, the others are: rigor mortis, livor mortis (lividity), decapitation, incineration, decomposition, evisceration of brain and/or heart.)

And in the setting of traumatic arrest (generally not considered survivable because it often implies massive internal blood loss), also: "obvious, devastating blunt or penetrating trauma to the head and is pulseless and apneic after opening airway", and "severe blunt or penetrating trauma and remains pulseless and apneic after the performance of all appropriate prehospital life-saving interventions for potentially reversible causes, including but not limited to, definitive airway management, external hemorrhage control, definitive chest decompression, and pericardiocentesis."