An authenticable digital code includes a printable medium, a machine-readable digital code, formed on the printable medium, that graphically represent information, and at least one security signature positioned relative to the machine-readable digital code. The security signature includes a fluorescent material that, when excited by light of a first wavelength, fluoresces and emits light at a second wavelength that is different from the first wave length. Authenticity of the authenticable digital code is determined by detecting, when the authenticable digital code is illuminated by light of the first wavelength, light of the second wavelength at a position relative to the machine-readable digital code.