Medium Density Overlay plywood is widely used for signs in 1/2" or 3/4" thickness. Also called Crezon, it is covered with a bonded layer of a stiff paper product providing for a smooth, longer lasting surface. It is then primed & painted.
 
MDO Engraved sign. 12" x 24" 
 
 
 
Comes in 3 sizes
 
12" x 24"
 
18" x 24"
 
24" x 36"