A laser inscription is a microscopic identifier, almost always a laboratory report number, sometimes a brand mark, occasionally an anti-fraud code, that has been applied along the girdle of a polished gemstone by a focused pulsed laser. The inscription is shallow (typically 5-15 microns deep) and is invisible to the unaided eye; it is read under a 10x loupe or in the laboratory microscope, and it ties an individual loose stone to its grading report in a way that does not depend on the integrity of the report's plip-paper or sealed packaging.

GIA introduced laser inscription as a routine service in the late 1990s, originally for diamonds, and the practice spread to coloured stones in the 2000s. Today GIA, IGI, HRD, AGL, GRS and Gubelin all offer inscription as a paid add-on to their grading reports. The most common content is the eight- or ten-digit report number, but laboratories will also inscribe brand names (the "Forevermark" or "Hearts on Fire" mark, for example), client logos, or arbitrary text strings up to a length determined by the available girdle length and font size.

From a trade standpoint, inscriptions are valuable for three reasons. They allow rapid verification of identity at the point of resale or trade-in, since the inscription can be matched to the laboratory's online database in seconds. They support fraud detection, because removal of the inscription requires re-polishing the girdle, which is detectable. And they help track stones through long supply chains, particularly in the lab-grown segment where laboratory laser-inscribes a "LABORATORY-GROWN" or "LG" prefix to the report number to avoid downstream substitution.

Inscription is normally non-destructive in the practical sense: the depth is well within the polishing tolerance of modern cutting, and a future re-cut or re-polish can remove the inscription without damaging the stone. For coloured stones with low thermal conductivity, the laboratory uses ultraviolet or femtosecond lasers to limit the heat-affected zone and avoid surface alteration adjacent to the marks.