The embodiments relate to a method for operating a medical appliance, (e.g., an angiography machine), in which an output data stream is produced with a first information item, and a first signature that is dependent on the first information item is embedded into the output data stream. The output data stream is supplied to an output apparatus and to a monitoring unit, wherein the first information item is presented by the output apparatus and the first signature is captured by the monitoring unit. An input is captured and is supplied to the monitoring unit. The input is coded on the basis of the first signature.