Abstract: The invention relates to an indicator comprising a substrate and an optical grating structure fabricated on the substrate, the grating structure being formed from an indicator material comprising a binder and deliquescent salt and varying in volume by the effect of moisture. Further, the invention relates to a method for fabricating an indicator wherein a substrate is coated by an indicator material forming an optical grating structure, and the optical grating structure is fabricated onto the substrate, and use of an indicator for detecting quality and/or authenticity. Furthermore, the invention relates to a package and a method for detecting a change induced by moisture without breaking the package.