(57) A franking machine having a printed head and a platen between which mail can be located for impressing a franking mark thereon, by relative movement of the head and platen, is characterised by the printing head including a retentive pad porous rubber stamp which is either impregnated with ink for life or has a reservoir and filler into which ink can be poured from time to time and is adapted to supply ink to the retentive pad.