I ALWAYS use hand signals during lighting storms. Should the aircraft get struck by lightning the shortest route to ground is via the headset through the headset person. The signal for engine fire is to hold one hand up illustrating the engine number, then make a horizontal figure 8 on your chest.
Obviously it is preferable by all parties to use a headset however in all cases this is not possible, but as long as both parties know and understand the signals/procedures they can be carried out safely.
I thought it was against regulations to use cellphones airside on the ramp?
