A method of identifying a source of a marking fluid applied to a person or an object comprises applying a marking fluid including one or more security markers to a person or an object and illuminating the applied marking fluid to excite the security markers. Photoluminescent emission from the security markers in response to the excitation is measured and compared with one or more pre-defined photoluminescent signatures associated with the source of the marking fluid. The source of the marking fluid is identified based on a match between the detected photoluminescent emission and at least one of the pre-defined photoluminescent signatures.