A very small, non-invasive inscription on a diamond, usually on the Girdle, using a very specialized laser device. Most gemological labs like GIA-GTL, AGSL, and EGL commonly laser inscribe their “Cert / Certificate” numbers on the girdle to help dealers and consumers identify a diamond and match it to a “cert”. Other examples are messages of love, the logo of the cutter on a Super Ideal Cut, date of your engagement, etc.
Laser inscriptions are semi-permanent. They will last forever undamaged, unless they are intentionally polished out by a diamond cutter.