Explanation: A Safety transmission refers to the international signal "SÉCURITÉ" (pronounced "Say-cure-e-tay"), which indicates a message concerning the safety of navigation or important meteorological warnings. This signal is used to alert all stations that a broadcast of critical information, not necessarily related to an immediate distress or urgency, but vital for general safety, is about to follow. Option B is incorrect because "PAN PAN" is an urgency signal, used when there is a serious condition concerning the safety of a vessel or person, but it is not immediately life-threatening (unlike "MAYDAY"). Option C describes general "health and welfare traffic," which is important communication during emergencies but doesn't define the specific "Safety transmission" signal itself. Option D uses a generic phrase "Safety Alert" which is not a recognized official radiotelephony signal for this purpose.