That because there are stupid criminals. Just looked at a number of mine...the stamp isnt very deep. There would be no problem at all getting rid of it entirely. Not that I am doing that of course as a law abiding gun owner!
I am surprised no one has corrected you on this. You could always file it off and send it to ATF. It won’t take long before they knock on your door (if it’s a recent purchase anyway). When ever you stamp or press metal, all the metal under the stamp is compressed. All they do is file the damage off and stick it under an X-ray. The pressed in digits are there. Theoretically you could remove enough metal, but depending on depth and the rounds you use that would be problematic.
The X-ray systems they use are commonly found in the aviation industry. Lots of aircraft metal parts and components get xrayed routinely. There’s even “true crime” shows that expressly mention this technique for crime solving regarding guns.
Not pulling your leg here. I have purchased and used those systems. Do you have any idea how human X-ray systems are checked for calibration? You radiograph a tool. The tool is metal and you read the depth of the data in the X-ray image. X-ray systems are built for this. So, Yeah Nah. Don’t ever suggest the old file the serial number off trick, unless you want them to get caught.
I do have some other suggestions that would likely work if you have any nefarious needs however!