Instrument for tattooing deserters, 1850 (c). 
Brass squared body and trigger with brass D plate and steel spikes. 
Engraved on side with manufacturers name, Savigny and Company, London. 
When a thumb piece at the other end of the cylinder is pulled the whole piston retracts and catches on a ratchet; when this is released by the depression of a steel lever, and internal spring forces the piston and spikes downwards.
Used for tattooing one initial D for deserter on the face or armpit.