Sign M1-H6b “Township Route Marker” from the Ohio Manual of Uniform Traffic Control Devices, with text converted to paths. The SDMM actually depicts File:Harmony Township Route 92, Morrow County, Ohio.svg, but this is a blank version of the shield.
"Guide Signs, Markers" in   (20 January 2006)  Sign Designs and Markings Manual (PDF), Ohio Department of Transportation
Ohio Department of Transportation