Nuclear warhead authentication is a crucial step in nuclear disarmament verification. Obviously, cheating of any kind has to be prevented. While several warhead authentication approaches rely on the passive emissions of a weapon’s fissile material, the uniqueness of these signatures has been brought into question repeatedly. It would hamper current verification efforts if malicious actors could replicate or fake these signatures with hoax objects. In this paper, we, therefore, evaluate the uniqueness of passive gamma emissions of nuclear weapons. Based on a notional nuclear weapon model available in public literature, we use computer simulations to obtain this model’s baseline gamma spectra as they would result from realistic measurements. Then we are looking for combinations of other relevant radioactive isotopes that could generate a similar spectrum and therefore be used to deceive verification measures. The analysis is repeated for multiple measurement technologies. Clearly, the higher the detector resolution is, the harder it is to develop suitable hoax objects. Yet, using lower resolutions has the benefit of providing intrinsic protection of highly sensitive warhead design information. Our results contribute to selecting adequate measurement approaches and discourage cheating more broadly.