Plasma marking is used for identification of plate and parts, for marking bend lines and weld points. The plasma marking process is available with all Ultra-Cut® plasma systems.
Ultra-Cut® systems are capable of plasma marking on all materials. The plasma marking process uses an inert gas (argon or nitrogen) to produce a clean, clear line which will remain visible indefinitely. Plasma marking uses the same consumable parts as the cutting process, so no consumable parts changes are necessary.
http://www.thermaldynamicsautomation.com/Plasma-Marking.php