Skull and bones.

A great bit of history Via: The Vintagent

"I believe this photograph shows the first instance of a 'skull and crossbones' (or Jolly Roger) logo on a motorcyclist's outfit. The photo was taken in Italy during WWI, and shows 'Renzo' on a Bianchi Model 500 A. Renzo ("waiting for action" it says on the back of the photo) was an Ardito (literally - 'audacious man'); the Arditi were the equivalent of Special Forces in the Italian Royal Army, created during a difficult period during the War for a specific job - to break a stalemate on the entrenched Italian Front. They were specially trained as an elite unit, with (according to 'Italian Arditi')"

"special recruitment procedures, training, arms, uniforms, priveleges, and benefits. For the first time, an Italian soldier was given concentrated, specific training, both psychological and physical; the Ardito also received the best available equipment and enjoyed superior living conditions. In order to counter the high casualty rate (!)... esprit de corps was very important..particular attention was focussed on comraderie and attitude, in order to motivtate the men and help them bear the psychological stress involved."