The invention concerns an anti-counterfeiting marker for providing variable entries (19) and for fixing them on a support (18) to be marked comprising: a sheet-like core (1) having at least a first colored effect (21), visible when illuminated by a predetermined light, and on the reverse side of the core (1), a brittle thickness (3) having a printing surface (4) designed to be damaged and peeled off the core (1) when scratched or erased in an attempt to counterfeit the variable entries (19), and including at least a second coloured effect (22) visible on the side of the printing surface (4) at least when illuminated by said predetermined light, and designed, by combination with the first colored effect (21), to produce a third colored effect (23). The invention also concerns the method for using such a marker and to the resulting marked medium.