diverging end 20 the pivot axis created by the shaft 26 generally extends horizontally as shown in fig2 the wind plate 24 has wind engaging surfaces and is bifurcated to form flanges 28 making the wind plate generally u201c u u201d shaped the wind plate flanges 28 are positioned on opposite sides of the diverging end 20 as shown the bifurcated portion is attached to the shaft 26 to allow the wind plate to pivot horizontally the wind plate is designed to be off balance the outer plate edge 30 is heavy with respect to the pivot so that gravitational forces will cause the outer wind plate edge 30 to assume the declining position shown in fig1 with the edge 46 of the wind plate 24 resting against the outer surface of diverging end 20 to limit downward rotation of the edge 30 when wind currents act on the sign the sign will rotate about the pivot so that the converging end 18 faces upwind also the wind plate 24 will rotate clockwise as shown in fig1 about axis 26 proportioned to wind velocity the wind plate 24 is off balance so that it will be lifted moved toward horizontal in proportion to wind velocity indicia 48 can be provided on the sign board 14 calibrated to wind speed and danger levels of gas exposure while an off balance wind plate configuration has less moving parts a resiliently urged wind plate can be used.