The image painted on wood pallet shows the bas-relief sandstone tablet known as the “Cincinnati Tablet” (found near downtown Cincinnati in 1841). The black portion of the painting represents the stone’s ink-stenciled areas. The grooves on the tablet’s backside suggest the stone was likely part of a tattoo kit. Other similar tablets are associated with Adena culture, 800BC – 100AD.
A good write up about the artifact, and similar Adena tablets, can be found here.