That's like the Spanish boundary stones. (I'm busy looking up earlier Roman stones ~ their later ones are dedicated to the god Terminus and are quite finished ~ many with carved heads on them).
This particular stone (even though we can't see the whole thing since the writer was more concerned with the word on it than the shape) appears to be a boundary marker.
Recently I plucked a file off the Zahi Hawass blog site showing one of the Akhetaten city boundary stones. Akhenaten decided he was divine, but set up the boundary stones beyond which he would never again go. My favorites though are the Pillars of Ashoka; two or three of them up in Afghanistan are in Aramaic.
This photo doesn’t do it justice. It’s quite large.