A marking device for mounting on the valve stem of a pressurized dispenser having a valve actuated by said valve stem, said container having a marking material and a propellant medium therein, said marking device comprising a mark-forming member, provided with an axial bore, said mark-forming member being adapted to be connected with the valve stem so that there is provided communication between the axial bore and a dispensing passage in the valve stem when the valve stem is actuated so as to dispense the marking material from the mark-forming member, said mark-forming member having a surface for contacting an object to be marked, said surface having disposed therein one or a plurality of open grooves extending radially from the axial bore to the outer periphery of the surface, characterized by the fact that said grooves (19; 19') have facing side walls (21, 22; 21', 22') angularly disposed with respect to each other so as to diverge in the direction of the surface (20; 20') in which the grooves (19, 19') are disposed.