Articles each having a reference mark located around a respective extension axis, are loaded on piece-holder assemblies distributed around a central axis of a rotatable drum, and each including a pair of spindles operable in rotation by a same motor, each around a respective longitudinal axis. The drum rotates about said central axis to transfer said piece-holder assembly to a printing station, where a printing pattern is formed on a side surface of each article driven in rotation by the respective spindle. Before transferring to the printing station, at least one of the articles is oriented around the respective spindle, to place the reference marks of the articles along a same angular orientation around the respective extension axes.