We disclose a method of tagging pharmaceutical and nutritional products with nanoparticles which include noble metals. The disclosure describes a plurality of nanoparticles each with either a different size and/or shape. The nanoparticles of different sizes and shapes are distinguishable using spectroscopic techniques because each is associated with different optical properties and have a different spectral signature. The different optical properties are at least due to the unique size or shape of the nanoparticles. Each of the plurality of nanoparticles may be associated with a different characteristic of the tagged pharmaceutical or nutritional product. The method includes mixing the nanoparticles with or adhering the nanoparticles to the tagged pharmaceutical or nutritional product. Two or more of the plurality of nanoparticles may be mixed with or adhered to the tagged pharmaceutical or nutritional product in a ratio and the ratio may be associated with a characteristic of the product.