Marine grade stainless steel should not be "engraved" or "etched", because any method that digs markings on the surface also removes an important invisible protective layer. This thin protective layer is composed of chromium oxide. Chromium oxide can be formed on the surface of stainless steel using a chemical immersion process that will also simultaneously remove any free iron from the surface. This process, known as passivation, is routinely applied to marine grade stainless steel products used in diving. The resulting clear, almost invisible, layer of chromium oxide prevents corrosion by stopping oxygen from reaching the underlying metal.
When that layer is removed, by engraving or just plain abrasion against another metal object, oxygen causes a chemical reaction on the now permanently exposed bare metal. That reaction is known as oxidation and the result can be corrosion damage. That's what happens when you mark stainless steel by laser engraving or laser etching, instead stainless steel must be laser annealed. Laser annealing does not remove the chromium oxide layer from the surface, yet leaves a permanent mark directly in the stainless steel.
Laser annealing modifies the molecular structure of the metal located under the clear chromium oxide layer. Using a laser, the metal is heated to a specific temperature for just a few milliseconds of time. This creates a change of color in the underlying metal that becomes visible beneath the clear protective layer on the surface. The correct amount of laser power for the correct amount of time is usually determined by trial because good results depend on the equipment and the composition of the stainless steel. Most importantly, no material is removed from the surface (as opposed to laser engraving). This means that the chromium oxide layer is unaffected, and the passivated stainless steel remains resistant to corrosion.