A softtag is a tag or a piece written on a wall with chalk. The first well known softtags were made by artists as Jean Michel Basquiat and Keith Haring in New York. The term softtag came in use in Oslo Norway in 2000, after an artist that did tags and pieces(grafitti)with chalk on walls around the city and signed them Softtag.
Keith Harings pieces on subway stations in New York. (Not all of them were made with chalk, but a few were).