1. A method for unambiguous marking of a product comprising: arranging unique features on the product or a packaging of the product or establishing unique features from at least a part of the product or the packaging thereof; digitizing the unique features and signing the digitized features with a private key; and arranging the signature of the digitized features on the product or a packaging of the product; wherein authenticity of the product can be determined by comparing the unique features with a decrypted signature of the digitized features, which signature is arranged on the product or the packaging thereof and decrypted with a public key; wherein the unique features are formed by means of three-dimensional structures or materials with optical properties that differ depending on a viewing angle, which structures or materials are optically detectable by a mobile phone, tablet PC or notebook, equipped with a camera; and wherein the digitized features are generated by an algorithm which is applied to at least two digital images of the unique features recorded with at least one digital camera from different viewing angles and/or with an illumination from different directions respectively.