A hypodermic syringe is provided with a colorant disposed at a readily accessible portion of the syringe so that when the colorant is touched against the skin of a patient, the colorant is transferred to the skin of the patient giving a visual indication of the point at which an injection has or will...http://www.google.co.uk/patents/US5192270?utm_source=gb-gplus-sharePatent US5192270 - Hypodermic syringe and a method for marking injections
