Abstract: An emergency signalling includes a sheet having an optically reflective face, for spreading upon an essentially horizontal surface, such that the optically reflective face is directed essentially upward. The sheet preferably has an emergency message on the optically reflective face in nonreflective letters. The apparatus also preferably includes a strobe light positioned on the sheet, an electric circuit, and an electric power source connected through the electric circuit to the strobe light. There is preferably a switch in the electric circuit for controlling the flow of electric current from the electric power source to the strobe light, and an optical sensor for operating the switch, such that the optical sensor closes the switch when light strikes the optical sensor and opens the switch no light strikes the optical sensor.