Dot peening provides an inexpensive way to permanently mark variose metal parts. Fixed mount and hand held units use air or electric to impact the vibrating pin creating the mark. Characters, Images and bar codes can be marked. For bar codes , unless painted after marking or other variable , lasers are a better choice.

Although a mature technology recent improvements have made it a good choice for Data Matrix DPM .

How does it work ?

Diffuse on axis light gets "trapped" inside the indentation thus not reflecting any light back to the camera, so it appears dark. Light hitting the surface reflects back to the camera making it look light.
Dot peen pin tip needs a reasonable sharp point with a cone angle of 30 degrees.
Dot depth is minimal and dot spacing is to under print. No touching or overlapping.
As always on data matrix confirm a Quiet Zone of two elements and no shadows from edges.