Geriaviator,
the Hercules airframe de-icing system was via bleed air from the engines. The prop de-icer was electrical. Smudge knows far more about this than I do. Often the first indication of ice was when the ALM reported it after one of his hourly scan checks.
The sound of ice being flung off the props and rattling on the fuselage could really get your attention.
Over on the Hercules thread there is a story of how one Hercules built up so much ice on the radome that the captain could only just trim out the resultant nose heavy situation.
In some parts of the world the contents of the water drain check was a highly prized item. Paraffin for fuel !