Abstract: Apparatus is provided for making a permanent mark on a hard surface such as glass or the like primarily for identification purposes. A hand held gun connected to a source of compressed air is adapted to drive a stream of abrasive particles towards a stenciling head on the marking end of the gun, which is held against the surface to be marked. The head carries interchangeable stencils located in the path of the stream of abrasive particles when the gun is actuated. When the stencil head of the gun is held flat against the surface which is to be marked and the gun actuated, the stencil indicia will be formed on the surface by the action of the abrasive particles abrading and etching the surface through the stencil openings. The stencil elements are formed by photo engraving techniques to produce sharp, precise characters and the elements themselves fit snugly together when assembled to prevent leakage between adjacent elements.