The Chalk Marker PC-5M from Uni Posca is a liquid crayon marker for all smooth surfaces, especially for glass, windows, mirrors, plastic, metal and black boards. The colour can be easily wiped off all smooth surfaces with a damp cloth. As it's waterproof, the chalk marker can also be used outdoors.
Here the set of eight markers in brilliant colors. 1.8 - 2.5mm round tip.