A customized CO(2) laser micromachining system was used for the generation of phase holographic structures directly on the surface of fused silica (HPFS(®)7980 Corning) and Borofloat(®)33 (Schott AG) glass. This process used pulses of duration 10µs and nominal wavelength 10.59µm. The pulse energy delivered to the glass workpiece was controlled by an acousto-optic modulator. The laser-generated structures were optically smooth and crack free. We demonstrated their use as diffractive optical elements (DOEs), which could be exploited as anti-counterfeiting markings embedded into valuable glass-made components and products.