If you ever worked in a shop with 20 other mechanics,most of whom had the same type of tools you do,you would understand why its sensible for a mechanic to mark his gear.
Let me clarify: I do not believe it is sensible to mark mechanics tools permanently. Besides defacing the tool, practically speaking, in most cases, I don't think it accomplishes anything. (You certainly can't identify the item by a simple glance.) I do not think it's sensible to engrave items, but I do think it's sensible to mark them for ID purposes.
I work professionally in environments where there are hundreds of workers and an extraordinary amount of very high value tools and equipment spread around, often over large areas, often remote or complicated areas, spread around over hours or days, and everyone scrambles to recover and account for everything in minutes, often in the dark. That being motion picture and television production. Grip, electricians, carpenters, rigging, camera support, props, stagehands, special effects, etc... Besides power tools, mechanics tools, carpentry tools, very specialized camera and lighting tools there hundreds of pieces of equipment and hardware from light fixtures and countless accessories, stands, stingers, rigging hardware, cribbage. All this stuff comes from different sources. Unloaded from dozens of trucks, often semi-trailers. A misplaced or lost lens for an HMI par light can cost $2000. A header cable $1200. A missing accessory for a quarter million dollar dolly big bucks, a one-of machined accessory for a million dollar camera setup big bucks. When it's time to strike a set or wrap a location, you recover everything, and lookout for everyone's stuff. How is everything marked or ID'd ? Mostly some type of color, such as paint or tape.