As I understand it Route 40 or The National Highway that would run the entire length of the USA is a sort of patchwork affair overlaying several other routes the farther west it goes.
In Ohio there were originally one of these stone markers every mile, about 225 in all. Now there are about 80 still in place. The Cumberland is the one in Maryland.
I am not sure what makes this one special but it looked big and mounted on a pedistal of smaller rocks so I stopped and got the pic.
About 15 miles from Zanesville there is a "bike path" on each side of the highway. This is really a glorified berm but compared to the rest of the road it is wonderful.