A tag with features to enable its authenticity to be determined includes a hidden code intermixed with a visible pattern such that the hidden code is not readily detectable under ambient light condition, without the use of a specially designed reader. In one embodiment the tag is formed with a first layer containing a hidden code, formed of reflective elements, which overlies a second layer which is designed to absorb light having a predetermined wavelength (e.g., IR light). The hidden code can be detected by projecting a light source having the predetermined wavelength (e.g., an IR source) at a predetermined angle on the tag and using a sensor to sense the reflection from the tag.