Wiktionary
isotopic signature
n. (context physics chemistry English) A set of ratios of the abundances of different isotopes of specified elements in a sample, used as a diagnostic test of the sample's origin, or of its age
Wikipedia
Isotopic signature
An isotopic signature (also isotopic fingerprint) is a ratio of non-radiogenic ' stable isotopes', stable radiogenic isotopes, or unstable radioactive isotopes of particular elements in an investigated material. The ratios of isotopes in a sample material are measured by isotope ratio mass spectrometry. See also isotope analysis.