Abstract: The disclosure is directed to systems, compositions and methods for tagging, identifying and authenticating bulk liquids. Specifically, the disclosure relates to methods, compositions and systems for selectively and specifically identifying bulk liquids as authentic using, as a tagging compound, photoluminescent carbon nanostructures (PCN's) suspended in a continuous phase that is thermodynamically incompatible with non-polar bulk liquid and/or substantially low concentration of PCNs; and incorporating the suspension into the liquid, wherein the suspension is incorporated at a concentration of continuous phase that is at least one of being below the solubility limit of the suspension's continuous phase in the bulk liquid and a concentration that cannot be observed unaided to the naked eye.