A multi-function signboard includes a frame seat, a light seat, a light diffusion strip, a display board, a circuit board and a power source portion. The frame seat is a hollow light impermeable structure having a top portion that sinks downward to form a frame rib, and a frame groove, and has two ends respectively connected to an end cap. The light seat is an elongate seat that has connecting wires connected to the circuit board, and a plurality of light emitting diodes of different colors arranged in sets of three to provide light of different colors. The light diffusion strip is a transparent elongated strip with a length equal to that of the light seat, and is disposed on the light seat. The light diffusion strip and the light seat are together disposed in the frame groove. The diffusion strip is provided with semi-circular holes corresponding to the light emitting diodes to diffuse the colored light emitted by the light emitting diodes. The display board is a transparent board structure that has a bottom portion inserted into the frame groove and supported by the light diffusion strip. The display board has a surface with an ornamental marking formed by words and/or devices to reflect the colored lights emitted from the light seat and the light diffusion strip to thereby achieve an ever-changing and multifarious lighting effect. The circuit board is a conventional control circuit that is provided in the frame seat and that has connecting wires connected to the light seat and a power source portion to control one or any two or all three in each set of light emitting diodes to flash alternately. The power source portion is adapted to supply power to the circuit board from an external power source to thereby control the light seat.