A preferred embodiment of the present invention is a mobile sign with a solar panel for warning motorists of highway problems. The mobile sign comprises support structure configured as a wheeled vehicle. In preferred embodiments, the sign panel comprises an enclosure or housing having a front transparent panel, a multiplicity of LED's in a matrixical arrangement for generating electronically changeable messages mounted in the enclosure and spaced from the front panel, and a pattern of opaque material, for example paint, applied on the exterior of the front transparent panel defining a plurality of windows for passing light therethrough. In a preferred embodiment, the windows will be in a matrixical arrangement comprising a plurality of rows and columns of individual LED's or rows and columns of groupings of LEDs.